1. Diabetes Mellitus

Diabetes mellitus encompasses a heterogeneous group of metabolic disorders characterized by chronic hyperglycemia. This section integrates the ADA Standards of Medical Care in Diabetes 2025, AACE/ACE 2024 Algorithm, and landmark cardiovascular outcome trials through 2025.

▼1.1 Classification & Pathophysiology

Type	Pathophysiology	Key Features	Prevalence
Type 1 DM	Autoimmune T-cell mediated β-cell destruction; absolute insulin deficiency	Positive islet autoantibodies (GAD65, IA-2, ZnT8, IAA); prone to DKA; onset before 40 yrs	5–10% of DM
Type 2 DM	Insulin resistance + progressive β-cell failure (ominous octet of DeFronzo)	Metabolic syndrome, obesity (80%), gradual onset; rarely DKA (except under stress)	90–95% of DM
LADA	Latent Autoimmune DM in Adults — slow autoimmune destruction	Adult onset, initially non-insulin requiring; GAD65+ (key); misdiagnosed as T2DM	5–10% of T2DM
MODY	Monogenic β-cell defects; autosomal dominant	Young onset, non-obese, family history; 14 subtypes (HNF1A, GCK, HNF4A most common)	1–5% of DM
GDM	Placental hormones → insulin resistance; unmasked β-cell insufficiency	Diagnosed ≥24 weeks; risk: obesity, PCOS, prior GDM, family history; 50% develop T2DM in 10 yrs	6–9% pregnancies
CFRD	Exocrine fibrosis → endocrine destruction + insulin secretory defect	Cystic fibrosis-related; insulin-requiring; unique: hypoglycemia alternates with hyperglycemia	40–50% adults w/ CF

🔑 Pearl: The "ominous octet" of T2DM pathophysiology (DeFronzo 2009): ↑hepatic glucose production, ↓insulin secretion, ↓incretin effect, ↑glucagon secretion, ↑lipolysis, ↑renal glucose reabsorption (SGLT2), neurotransmitter dysfunction, ↓peripheral glucose uptake. Each is a therapeutic target.

▼1.2 Diagnosis & Glycemic Monitoring — ADA 2025

Test	Normal	Prediabetes	Diabetes	Notes
FPG (fasting plasma glucose)	<100 mg/dL	100–125 (IFG)	≥126 mg/dL	Requires 8h fast; confirm with repeat or 2nd test
2h-PG (75g OGTT)	<140 mg/dL	140–199 (IGT)	≥200 mg/dL	Gold standard for GDM screening (24–28 wks)
HbA1c	<5.7%	5.7–6.4%	≥6.5%	No fasting needed; unreliable in hemoglobinopathies, hemolytic anemia, CKD
Random PG + symptoms	—	—	≥200 mg/dL + polyuria/polydipsia/weight loss	No confirmation needed if classic symptoms present

ADA 2025 Glycemic Targets:

Parameter	General Target	Stricter (if safe)	Relaxed (high-risk)
HbA1c	<7.0%	<6.5% (young, newly diagnosed, no hypoglycemia risk)	<8.0% (elderly, frail, hypoglycemia unawareness)
Pre-meal glucose	80–130 mg/dL	70–110	90–150
Post-meal (2h peak)	<180 mg/dL	<140	<200
TIR (CGM, 70–180 mg/dL)	>70%	>80%	>50%
TAR (>180 mg/dL)	<25%	<20%	<35%
TBR (<70 mg/dL)	<4%	<1%	<4%

🏆 High-Yield: CGM Metrics (ADA/EASD 2025)

TIR >70% ≈ HbA1c ~7%; each 10% TIR improvement = ~0.5% HbA1c reduction
GMI (Glucose Management Indicator) = 3.31 + 0.02392 × mean glucose — estimates HbA1c from CGM
CGM now recommended for all T1DM and insulin-treated T2DM (ADA 2025 Standard of Care)
Flash CGM (FreeStyle Libre) acceptable for lower-risk patients; real-time CGM preferred for hypoglycemia unawareness

▼1.3 Type 1 Diabetes — Insulin Therapy & AID Systems

Insulin	Onset	Peak	Duration	Notes
Lispro (Humalog), Aspart (NovoLog), Glulisine (Apidra)	5–15 min	1–2h	3–5h	Rapid-acting analogs; use with meals
Ultra-rapid: Faster aspart (Fiasp), Lispro-aabc (Lyumjev)	2–5 min	1h	3–5h	Even faster onset; useful for post-meal dosing
Regular (Humulin R, Novolin R)	30–60 min	2–4h	6–8h	Only insulin for IV infusion (DKA protocol)
NPH (Humulin N)	2–4h	4–10h	12–18h	Intermediate; peaking → nocturnal hypoglycemia risk
Glargine U-100 (Lantus), Detemir (Levemir)	2–4h	Relatively peakless	20–24h (Glargine), 12–20h (Detemir)	Long-acting; once or twice daily
Glargine U-300 (Toujeo)	6h	Peakless	36h	Lower hypoglycemia vs U-100; 3× concentration
Degludec U-100/U-200 (Tresiba)	1h	Peakless	>42h	Ultra-long; lowest hypoglycemia among basals; flexible dosing

Basal-Bolus Therapy: Total Daily Dose (TDD) = 0.5–0.7 units/kg/day. 50% basal : 50% bolus. Correction factor = 1800/TDD (for regular) or 1700/TDD (for analogs).

AID System (Hybrid Closed Loop)	Algorithm	Key Outcome	Trial
MiniMed 780G (Medtronic)	Auto-basal + auto-correction bolus; target 100 mg/dL	TIR 79%, HbA1c 7.2%→6.9%	ATTD 2023
Control-IQ (Tandem + Dexcom G6)	Model predictive; auto-basal + sleep mode	TIR +11% vs SAP; HbA1c −0.33%	PIDS 2019, NEJM
OmniPod 5 (tubeless + Dexcom G6)	SmartBolus + auto-basal; target 110–150 mg/dL adjustable	TIR 74%, TBR ↓50%	PRISM 2022
iLet Bionic Pancreas	Insulin-only; self-initializing algorithm	HbA1c −0.5% vs standard care; less user burden	NEJM 2023

🔑 Pearl: Teplizumab (Tzield) — FDA approved 2022. Anti-CD3 mAb (anti-T-cell). 14-day IV course delays T1DM onset by median 2 years in Stage 2 (autoantibody+, dysglycemia, no symptoms) individuals. NNT = 2.1 at 5 years. Screen first-degree relatives with islet autoantibody testing. TrialNet Teplizumab, NEJM 2019

▼1.4 Type 2 DM — ADA 2025 Treatment Algorithm

The ADA 2025 algorithm is complication-centric, not glucose-centric. Drug selection depends on: HbA1c level, comorbidities (CVD, HF, CKD), weight considerations, hypoglycemia risk, cost, and patient preference.

Clinical Scenario	First Add-On After Metformin	Rationale
Established ASCVD	GLP-1 RA (with proven CV benefit) or SGLT2i	CV mortality reduction (LEADER, EMPA-REG, SUSTAIN-6)
Heart Failure (HFpEF or HFrEF)	SGLT2i (empagliflozin, dapagliflozin)	HF hospitalization ↓ 25–35% (EMPEROR-Reduced, DAPA-HF)
CKD (eGFR ≥20, UACR ≥200)	SGLT2i + Finerenone	CREDENCE, DAPA-CKD, FIDELIO-DKD; renal protection + CV benefit
Weight loss priority	Tirzepatide (GIP/GLP-1 RA) or Semaglutide	−15% to −22% body weight; SURMOUNT-1, STEP-1
Minimize hypoglycemia	DPP-4i, SGLT2i, GLP-1 RA, TZD	Low intrinsic hypoglycemia risk (no insulin secretagogue effect)
Cost concern	Sulfonylurea, TZD (pioglitazone), NPH insulin	Generic availability; low cost per month
HbA1c very high (>10%) or symptomatic	Early insulin (basal) ± GLP-1 RA	Glucose toxicity; rapid reduction needed

🏆 High-Yield: MACE Definition in CV Outcome Trials

3-point MACE: CV death + non-fatal MI + non-fatal stroke — primary endpoint in most CVOT
4-point MACE: adds hospitalization for unstable angina
GLP-1 RA benefit is mainly on atherosclerotic events (MI, stroke); SGLT2i benefit mainly on HF and renal
Both classes now recommended independently of metformin when CVD/HF/CKD present (ADA 2025)

▼1.5 GLP-1 Receptor Agonists — Pharmacology & Key Trials

Drug	Route/Frequency	HbA1c ↓	Weight ↓	CV Outcome Trial	Key MACE Finding
Exenatide (Byetta) 5–10 mcg BID SC	SC BID	0.8–1.0%	−2–3 kg	EXSCEL (2017)	Non-inferior (neutral); HR 0.91 (NS)
Exenatide XR (Bydureon) 2 mg weekly	SC weekly	1.0–1.5%	−2 kg	EXSCEL (2017)	Non-inferior
Liraglutide (Victoza) 1.2–1.8 mg daily	SC daily	1.0–1.5%	−3 kg	LEADER 2016, NEJM	Superior: MACE HR 0.87 (13% ↓); CV death HR 0.78
Semaglutide (Ozempic) 0.5–2 mg weekly	SC weekly	1.5–2.0%	−5–6 kg	SUSTAIN-6 2016, NEJM	Superior: MACE HR 0.74; ↓stroke (39%), ↓MI (26%)
Oral Semaglutide (Rybelsus) 7–14 mg daily	PO daily	1.2–1.5%	−4 kg	PIONEER 6 (2019)	Non-inferior; MACE HR 0.79 (NS)
Dulaglutide (Trulicity) 0.75–4.5 mg weekly	SC weekly	1.0–1.6%	−2–3 kg	REWIND 2019, Lancet	Superior: MACE HR 0.88; primary/secondary prevention
Tirzepatide (Mounjaro) 5–15 mg weekly	SC weekly	1.8–2.4%	−7–12 kg	SURPASS-CVOT 2024, NEJM	Superior: MACE HR 0.85 (15% ↓)
Semaglutide 2.4 mg (Wegovy) obesity dose	SC weekly	—	−15–17%	SELECT 2023, NEJM	Superior: MACE HR 0.80 (20% ↓) in overweight/obese without DM

Mechanism: GLP-1 RA → GLP-1 receptor agonism → ↑glucose-dependent insulin secretion, ↓glucagon, ↓gastric emptying, ↑satiety (hypothalamic action), ↓hepatic glucose production. Tirzepatide additionally activates GIP receptor → synergistic weight loss + β-cell preservation.

🔑 Pearl: GLP-1 RA contraindications: Personal/family history of medullary thyroid carcinoma or MEN2 (due to C-cell hyperplasia in rodents — human risk uncertain but precautionary); severe gastroparesis; pancreatitis history (relative). Main side effects: nausea/vomiting (dose-limiting in 10–20%); rare pancreatitis (no proven causal link in RCTs); gallbladder disease (↑with weight loss). GLP-1 RA do NOT cause hypoglycemia alone.

▼1.6 SGLT2 Inhibitors — Pharmacology & Key Trials

Drug	Dose	HbA1c ↓	Weight ↓	eGFR Min	Key Trials	Outcomes
Empagliflozin (Jardiance)	10–25 mg daily	0.8%	−2 kg	≥20 (CKD/HF indication)	EMPA-REG 2015, EMPEROR-Reduced, EMPEROR-Preserved	CV death ↓38%; HHF ↓35%; renal progression ↓44%
Canagliflozin (Invokana)	100–300 mg daily	0.8–1.0%	−2–3 kg	≥30 (glycemic); ≥20 (renal)	CANVAS 2017, CREDENCE 2019	MACE ↓14%; renal composite ↓30%; CREDENCE: eGFR decline ↓40%
Dapagliflozin (Farxiga)	10 mg daily	0.8%	−2 kg	≥25 (DM); ≥25 (HF/CKD)	DECLARE-TIMI 2019, DAPA-HF 2019, DAPA-CKD 2020	HHF ↓27%; HFrEF: death/worsening HF ↓26%; CKD: renal/CV composite ↓39%
Ertugliflozin (Steglatro)	5–15 mg daily	0.7%	−2 kg	≥45	VERTIS-CV 2020	Non-inferior for MACE; HHF ↓30%

🏆 SGLT2i Side Effects & Safety

Genital mycotic infections (Candida): most common; F > M; treat with antifungals
UTI: modest ↑ risk; educate on genital hygiene
DKA: Euglycemic DKA — rare but serious; risk: T1DM (caution!), low carb diet, fasting, surgery, illness → hold SGLT2i 3–5 days before elective surgery
Canagliflozin: ↑lower limb amputation (CANVAS; NNH=345); Fournier's gangrene (rare, class effect)
Volume depletion/hypotension: especially with diuretics; caution in elderly
eGFR drop: Acute, hemodynamic (like ACEi initiation) — NOT structural injury; benign; does NOT mandate drug cessation if stable
SGLT2i now approved for CKD, HFpEF, HFrEF regardless of T2DM status

▼1.7 Microvascular Complications

Diabetic Nephropathy (Diabetic Kidney Disease)

Stage	eGFR	UACR	Management
G1A1 (hyperfiltration)	>90	<30 mg/g	Optimal glycemia, BP <130/80, ACEi/ARB if UACR rising
G2A2 (microalbuminuria)	60–89	30–299	ACEi/ARB mandatory; SGLT2i if eGFR ≥20; GLP-1 RA
G3A3 (macroalbuminuria)	30–59	≥300	Add Finerenone (FIDELIO-DKD: ↓renal composite 18%); avoid NSAIDs, contrast
G4–G5	<30	Variable	Nephrology referral; prepare for RRT; insulin dose adjustment needed

Finerenone (nonsteroidal MRA) — FIDELIO-DKD (2020, NEJM) + FIGARO-DKD (2021): ↓renal composite 18%, ↓MACE 14% in T2DM+CKD on RAAS blockade. Now recommended as add-on after SGLT2i (ADA 2025).

Diabetic Retinopathy

Leading cause of blindness in working-age adults. Classified: Non-proliferative (NPDR: mild/moderate/severe) → Proliferative (PDR).
Screening: T1DM — annual eye exam starting 5 years after diagnosis; T2DM — at diagnosis, then annually.
Treatment: Optimal glycemic control (DCCT/EDIC: HbA1c 7% vs 9% → 76% retinopathy reduction); laser photocoagulation (PDR); intravitreal anti-VEGF (ranibizumab, aflibercept) for DME (diabetic macular edema).

Diabetic Neuropathy

Type	Features	Treatment
Distal symmetric polyneuropathy (DSPN)	Length-dependent; stocking-glove; burning pain, numbness; ↓vibration, proprioception	Pain: Pregabalin, Duloxetine (FDA approved); Gabapentin, TCAs; topical capsaicin
Autonomic neuropathy — Cardiac	Resting tachycardia, fixed HR, orthostatic hypotension, silent MI	Midodrine, fludrocortisone (for OH); β-blockers cautiously
Autonomic — GI (gastroparesis)	Early satiety, nausea, erratic glucose; nuclear gastric emptying scan	Metoclopramide (short-term); erythromycin; dietary modification; gastric stimulator
Autonomic — Genitourinary	Neurogenic bladder, erectile dysfunction, retrograde ejaculation	PDE5 inhibitors (sildenafil) for ED; self-catheterization for neurogenic bladder
Mononeuropathy/cranial nerve	CN III palsy (with pupil sparing in DM — vs aneurysm which spares pupil less); foot drop (peroneal)	Usually self-limited; supportive

🔑 Pearl: Diabetic CN III palsy — pupil SPARING (ischemic; outer pupillomotor fibers preserved). Aneurysmal CN III palsy — pupil INVOLVED (compressed from outside). This distinction is critical in emergency assessment.

▼1.8 Special Populations — CKD, Heart Failure, Elderly, Pregnancy

Population	HbA1c Target	Preferred Agents	Avoid
CKD eGFR 30–60	<7–8%	SGLT2i (if eGFR≥20), GLP-1 RA (no dose adj), DPP-4i (dose adjust), Insulin	Metformin hold if eGFR<30; SGLT2i ineffective glycemically <30 but renal/CV benefit persists
CKD eGFR <30 (non-dialysis)	<8%	Insulin (dose ↓ — renal clearance ↓); Repaglinide; Linagliptin (no renal dose adj)	Metformin CI; most SUs (hypoglycemia); Canagliflozin; Exenatide (if eGFR<30)
Heart Failure (any EF)	<8% (flexible)	SGLT2i — primary choice; GLP-1 RA (neutral on HF); DPP-4i except Saxagliptin	Thiazolidinediones (TZD) — fluid retention, worsen HF; Saxagliptin (SAVOR-TIMI: ↑HHF)
Elderly (≥75 or frail)	<7.5–8.5%	DPP-4i (well tolerated); SGLT2i (low hypoglycemia); Basal insulin with caution	Sulfonylureas (prolonged hypoglycemia); Tight control (hypoglycemia → falls/fractures/CV events)
Pregnancy (GDM)	FPG<95, 1hPP<140, 2hPP<120 mg/dL	Medical nutrition therapy first; Insulin (drug of choice); Metformin (2nd line — crosses placenta); Glyburide (less preferred)	All other oral agents, GLP-1 RA, SGLT2i — insufficient safety data

▼1.9 Inpatient Glycemic Management

ADA 2025 Targets — Hospitalized Patients: Non-ICU: 140–180 mg/dL; ICU: 140–180 mg/dL (no benefit <140; NICE-SUGAR: intensive control → ↑mortality). Target 100–140 mg/dL only if easily achieved without hypoglycemia.

Preferred regimen: Basal-bolus-correction (scheduled) insulin > sliding scale alone (sliding scale = reactive, not proactive; associated with worse outcomes)
Hold metformin: contrast, surgery, illness with dehydration, AKI
Hold SGLT2i: NPO status, surgery, illness (euglycemic DKA risk)
GLP-1 RA: generally continued in stable patients; hold if NPO/poor oral intake (nausea risk)
Steroid-induced hyperglycemia: typically post-lunch surge (intermediate-acting AM steroid) → NPH in AM or ↑mealtime insulin; may need TDD ↑30–50%
Perioperative: target 140–180 mg/dL intraoperatively; insulin infusion for major cardiac/vascular surgery

📚 Key References — Section 1

ADA Standards of Care 2025. Diabetes Care 2025;48(Suppl 1):S1–S352.
EMPA-REG OUTCOME. Zinman B et al. NEJM 2015;373:2117–2128.
LEADER. Marso SP et al. NEJM 2016;375:311–322.
SUSTAIN-6. Marso SP et al. NEJM 2016;375:1834–1844.
CREDENCE. Perkovic V et al. NEJM 2019;380:2295–2306.
DAPA-HF. McMurray JJV et al. NEJM 2019;381:1995–2008.
SELECT (Semaglutide). Lincoff AM et al. NEJM 2023;389:2221–2232.
SURPASS-CVOT (Tirzepatide). Bhatt DL et al. NEJM 2024.
FIDELIO-DKD (Finerenone). Bakris GL et al. NEJM 2020;383:2219–2229.
TrialNet Teplizumab. Herold KC et al. NEJM 2019;381:603–613.

2. Thyroid Disorders

Thyroid disease is the second most common endocrine disorder. This section covers interpretation of thyroid function tests, hypothyroidism, hyperthyroidism, thyroiditis, thyroid nodules, thyroid cancer, and thyroid disease in pregnancy — integrating the ATA 2023 Hyperthyroidism Guidelines, ATA 2015 Thyroid Nodule Guidelines (2023 updates), and ATA 2017 Hypothyroidism Guidelines.

▼2.1 Thyroid Function Tests — Interpretation

TSH	Free T4	Free T3	Diagnosis	Next Step
↑ (>4.5 mIU/L)	Low	Low/normal	Primary hypothyroidism	Start levothyroxine; check TPO-Ab
↑ (4.5–10)	Normal	Normal	Subclinical hypothyroidism	Repeat in 3–6 months; treat if TSH>10, symptomatic, TPO+, pregnancy
↓ (<0.4)	↑	↑	Primary hyperthyroidism (overt)	TRAb, thyroid scan, radionuclide uptake
↓ (<0.4)	Normal	Normal/↑	Subclinical hyperthyroidism	Repeat 4–6 weeks; treat if TSH<0.1, age>65, AF, osteoporosis
↓ or normal	↓	Low	Central (secondary/tertiary) hypothyroidism	MRI pituitary; check cortisol first (secondary AI may be concurrent)
↑ very high (>100)	↑↑	↑↑	TSH-secreting pituitary adenoma (TSHoma)	MRI pituitary; α-subunit; ratio α-subunit/TSH

🔑 Pearl: When TSH is low but fT4 is normal, check fT3 — T3 toxicosis (elevated T3 with normal T4) occurs early in Graves' disease or toxic nodule. fT3 > fT4 ratio suggests Graves' (high T3/T4 ratio > 20) vs thyroiditis (where ratio typically <20, as preformed T4 is released preferentially).

▼2.2 Hypothyroidism — Diagnosis, Causes & Treatment

Cause	Frequency	Key Features	Antibodies
Hashimoto's thyroiditis (chronic autoimmune)	Most common (developed world)	Goiter (early) → atrophic; women 7:1; associated with T1DM, celiac, Addison's, vitiligo	TPO-Ab (>95%), TgAb (60–80%)
Post-thyroidectomy	Common	Permanent; dose depends on residual tissue; higher dose if thyroid cancer	None relevant
Post-RAI	Common	Dose-dependent; often permanent; onset 2–6 months after treatment	TRAb may persist
Drug-induced	10–15%	Amiodarone (iodine load → Wolff-Chaikoff); Lithium (blocks thyroid hormone release); Interferon-α; Checkpoint inhibitors (immune-related thyroiditis)	Variable
Iodine deficiency	Most common worldwide	Goiter; cretinism if congenital; endemic	None specific
Secondary (pituitary)	Rare	Low/normal TSH + low fT4; other pituitary deficiencies; no goiter	None

Levothyroxine (LT4) Therapy:

Full replacement dose: ~1.6 mcg/kg/day. Elderly or IHD: start 25–50 mcg daily, titrate slowly.
Take on empty stomach, 30–60 min before breakfast (or bedtime — equally effective; NEJM 2010 Bolk et al).
Monitor TSH 6–8 weeks after dose change. Half-life of LT4 = 7 days.
Higher doses needed: pregnancy (+30–50%); malabsorption (celiac, short bowel); drugs (PPI, calcium, iron, cholestyramine reduce absorption — separate by 4h); enzyme inducers (rifampin, phenytoin, carbamazepine).
TSH target: generally 0.5–2.5 mIU/L; thyroid cancer surveillance: TSH <0.1 (high-risk) or 0.5–2.0 (low-risk).

🏆 LT4 + LT3 Combination Therapy

Some patients remain symptomatic on LT4 with normal TSH ("residual symptoms")
LT4+LT3 combination: controversial; ATA does not routinely recommend but may be tried in symptomatic patients with normal TSH
LT3 (liothyronine) has short half-life (1 day) → peaks/troughs; sustained-release LT3 under investigation
Desiccated thyroid extract (DTE, Armour Thyroid): contains T4+T3; some patients prefer; supraphysiologic T3 concern

▼2.3 Hyperthyroidism — Graves' Disease, Toxic Nodular Goiter

Cause	RAIU	Scan Pattern	TRAb	Treatment of Choice
Graves' disease	↑↑ (35–95%)	Diffuse homogeneous uptake	Positive (95%)	RAI, ATD (methimazole), or thyroidectomy
Toxic multinodular goiter (Plummer)	↑ (20–60%)	Patchy, multiple hot nodules	Negative	RAI or thyroidectomy preferred (ATD as bridge)
Toxic adenoma (hot nodule)	↑ in nodule only	Single hot nodule; suppressed rest	Negative	RAI or thyroidectomy; ATD as bridge
Subacute thyroiditis (de Quervain)	↓ (<5%)	Low/absent	Negative	NSAIDs; steroids if severe; β-blocker for symptoms; self-limited
Amiodarone-induced Type 1	Normal/↑	Variable	Negative	High-dose methimazole; continue amiodarone if necessary
Amiodarone-induced Type 2	↓	Low uptake	Negative	Prednisolone 40 mg daily; ± stop amiodarone if possible

Antithyroid Drugs (ATD)

Drug	Dose	Mechanism	Advantages	Side Effects
Methimazole (MMI) (Tapazole)	10–40 mg daily (once or divided)	Blocks TPO → inhibits organification and coupling	Once daily; faster remission; fewer SE overall	Agranulocytosis (0.2–0.5%); hepatocellular damage (rare); rash, arthralgias
Propylthiouracil (PTU)	100–300 mg TID	Blocks TPO + peripheral T4→T3 conversion	Drug of choice in 1st trimester pregnancy; thyroid storm	Agranulocytosis; fulminant hepatic necrosis (rare but fatal); vasculitis (ANCA+)

🔑 Agranulocytosis Warning: Check CBC if fever/sore throat during ATD therapy. Stop drug immediately. Agranulocytosis: ANC <500/mm³. Do NOT switch between MMI and PTU — cross-reactivity. Treat with G-CSF + antibiotics. Patients must be counseled to seek immediate care for fever/pharyngitis.

Graves' Disease — Special Considerations

Graves' ophthalmopathy (GO): Occurs in 25–50%; proptosis, periorbital edema, diplopia, corneal exposure. Severity graded by EUGOGO. Active moderate-severe GO → IV methylprednisolone pulses (EUGOGO protocol); teprotumumab (IGF-1R inhibitor, FDA 2020) for moderate-severe active GO; orbital decompression for severe/vision-threatening.
TRAb monitoring: TRAb titer at diagnosis; repeat at end of 12–18 months ATD. Remission after ATD: 40–50% at 12–18 months. Predictors of remission: small goiter, mild disease, low TRAb, normalization of TRAb on therapy.
Definitive therapy (RAI): Standard in non-pregnant adults; must rule out pregnancy; use MMI if very symptomatic first (stop MMI 5–7 days before RAI). Avoid RAI if moderate-severe active GO (may worsen GO — use selenium + prophylactic steroids if RAI chosen).

▼2.4 Thyroid Nodules — TIRADS & Bethesda Classification

Thyroid nodules are palpable in 5% but detectable by ultrasound in 50% of adults. Key question: is it malignant? (5–15% malignancy rate in referred nodules).

ACR TIRADS Category	Score	Malignancy Risk	FNA Threshold
TR1 — Benign	0	0%	No FNA
TR2 — Not suspicious	2	<2%	No FNA
TR3 — Mildly suspicious	3	~5%	FNA ≥2.5 cm; follow ≥1.5 cm
TR4 — Moderately suspicious	4–6	5–20%	FNA ≥1.5 cm; follow ≥1.0 cm
TR5 — Highly suspicious	≥7	>20%	FNA ≥1.0 cm; follow ≥0.5 cm

Bethesda System for Cytopathology (TBSRTC):

Category	Malignancy Risk	Management
I — Non-diagnostic	5–10%	Repeat FNA with ultrasound guidance
II — Benign	<3%	Follow-up imaging; no surgery
III — AUS/FLUS	6–18%	Repeat FNA or molecular testing (ThyroSeq v3, Afirma GSC)
IV — FN/Suspicious FN	10–40%	Molecular testing or diagnostic lobectomy
V — Suspicious malignancy	45–75%	Near-total thyroidectomy or lobectomy
VI — Malignant	94–96%	Thyroidectomy ± RAI ± EBRT per cancer type

🔑 Pearl — Molecular Testing: For Bethesda III/IV, molecular testing can stratify risk to avoid unnecessary surgery. Afirma GSC (gene expression classifier): "Benign" result → 3% malignancy risk (rule-out); "Suspicious" → 50% malignancy risk. ThyroSeq v3: molecular panel detecting mutations (BRAF, RAS, RET, NTRK, PAX8-PPARγ); NPV 97%, PPV 66%. These tests complement but do not replace clinical judgment.

▼2.5 Thyroid Cancer — Classification & Management

Type	%	Origin	Marker	Prognosis	Treatment
Papillary (PTC)	80–85%	Follicular cell	Thyroglobulin	Excellent (20-yr OS ~95%)	Thyroidectomy ± RAI ± TSH suppression; BRAF V600E → ↑recurrence risk
Follicular (FTC)	10–15%	Follicular cell	Thyroglobulin	Good (hematogenous mets — lung, bone)	Thyroidectomy + RAI; RAS mutations common
Medullary (MTC)	3–5%	Parafollicular C-cells	Calcitonin, CEA	Intermediate (10-yr OS ~75%); 25% familial (RET)	Total thyroidectomy + central neck dissection; Vandetanib, Cabozantinib (advanced MTC)
Anaplastic (ATC)	<2%	Follicular cell (dedifferentiated)	None specific	Dismal (median OS 6 months); most lethal solid tumor	BRAF V600E+ → Dabrafenib + Trametinib (FDA approved 2018); palliative chemo/RT

RAI Eligibility: Iodine-131 ablation: after total thyroidectomy in intermediate/high-risk differentiated TC. Low-risk (T1a, N0, M0, intrathyroidal) → may not need RAI (ATA 2015). Stimulation with recombinant TSH (Thyrogen) or thyroid hormone withdrawal to ↑TSH before RAI.

🏆 Medullary Thyroid Cancer — Genetic Testing

All MTC patients must undergo germline RET mutation testing (25–30% are hereditary)
MEN2A: RET codon 634 (most common) → MTC + pheochromocytoma + primary HPT
MEN2B: RET codon 918 → most aggressive MTC; marfanoid habitus, mucosal neuromas; no HPT
FMTC (familial MTC): RET mutations; MTC only; lower penetrance; least aggressive
Prophylactic thyroidectomy timing based on RET codon: very high-risk (918) → <6 months; high-risk (634) → <5 years; moderate-risk → calcitonin-guided
First-degree relatives: screen with germline RET; if negative, no further surveillance needed

▼2.6 Thyroiditis — Classification & Management

Type	Pain	Course	TSH/fT4	RAIU	Rx
Hashimoto's (chronic lymphocytic)	No	Chronic → hypothyroidism	↑TSH (eventually)	Variable (normal/↑)	LT4 when hypothyroid
De Quervain's (subacute granulomatous)	Yes +++	Triphasic: hyper → hypo → normal; 4–6 months total; post-viral	↓TSH → ↑TSH → normal	↓↓ (<5%)	NSAIDs; prednisone 40 mg if severe; β-blocker for hyperthyroid phase; LT4 if prolonged hypothyroid
Postpartum thyroiditis	No	Triphasic (3m hyper → 6m hypo → recovery); 5–10% of postpartum women; TPO-Ab+	↓ then ↑	↓	β-blocker (hyper phase); LT4 if hypothyroid and symptomatic; may recur with each pregnancy
Silent (painless) thyroiditis	No	Same as postpartum but not related to pregnancy; TPO-Ab+	↓ then ↑	↓	Same as postpartum
Drug-induced (checkpoint inhibitors)	No	Hyperthyroid phase → permanent hypothyroidism common	↓ then ↑	↓	Hold immunotherapy for severe grade; steroids rarely needed; LT4 for hypothyroidism

▼2.7 Thyroid Disease in Pregnancy

Normal thyroid changes in pregnancy: ↑TBG (estrogen) → ↑total T4; ↑hCG (TSH receptor stimulation) → ↓TSH in 1st trimester; ↑renal iodine clearance → relative iodine deficiency; thyroid volume ↑10–15%.

Parameter	1st Trimester	2nd Trimester	3rd Trimester
TSH reference range	0.1–2.5 mIU/L	0.2–3.0 mIU/L	0.3–3.0 mIU/L
fT4	Upper normal (hCG stimulation)	Slightly lower	Slightly lower

Hypothyroidism in pregnancy: TSH >2.5 in 1st trimester → treat with LT4. Untreated → ↑miscarriage, preterm birth, impaired fetal neurodevelopment (fetus depends on maternal T4 until 12 weeks). LT4 dose ↑ ~30% at confirmed pregnancy (add 2 extra doses/week empirically).
Hyperthyroidism in pregnancy: MMI teratogenic in 1st trimester (choanal atresia, aplasia cutis) → use PTU in 1st trimester → switch to MMI in 2nd trimester (PTU hepatotoxicity risk). Avoid RAI (absolutely contraindicated in pregnancy). Target TSH low-normal.
TRAb (TSH receptor antibodies): Cross placenta → fetal/neonatal hyperthyroidism. Check TRAb at 18–22 weeks in treated Graves' patients; elevated TRAb → monitor fetus (fetal HR, growth).
Neonatal hypothyroidism: Newborn screening mandatory; universal TSH at 24–72h of life.

📚 Key References — Section 2

ATA Guidelines — Hyperthyroidism 2016 (updated 2023). Ross DS et al. Thyroid 2016;26:1343–1421.
ATA Guidelines — Thyroid Nodules & DTC 2015. Haugen BR et al. Thyroid 2016;26:1–133.
ATA Guidelines — Hypothyroidism 2014. Garber JR et al. Thyroid 2012;22:1200–1235.
EUGOGO — Graves' Ophthalmopathy 2021. Bartalena L et al. Eur Thyroid J 2021.
Teprotumumab (OPTIC). Smith TJ et al. NEJM 2020;382:341–352.
ACR TIRADS 2017. Tessler FN et al. J Am Coll Radiol 2017;14:587–595.

3. Adrenal Disorders

Adrenal disorders span excess and deficiency states of cortisol, aldosterone, androgens, and catecholamines. This section integrates the Endocrine Society 2022 Cushing's Guidelines, Endocrine Society 2024 Primary Hyperaldosteronism Guidelines, and current PPGL management.

▼3.1 Adrenal Physiology & HPA Axis

Zone	Hormone	Regulation	Clinical Deficiency	Clinical Excess
Zona glomerulosa (outer)	Aldosterone (mineralocorticoid)	Angiotensin II, ↑K+, ACTH (minor)	Salt wasting, hyperkalemia (Addison's)	Primary hyperaldosteronism (Conn's)
Zona fasciculata (middle)	Cortisol (glucocorticoid)	ACTH (CRH→ACTH→cortisol); circadian (AM peak)	Adrenal insufficiency	Cushing's syndrome
Zona reticularis (inner)	DHEA, DHEAS, androstenedione (androgens)	ACTH; pubertal adrenarche	Loss of adrenal androgens (AI)	Congenital adrenal hyperplasia (CAH), adrenal carcinoma
Adrenal medulla	Epinephrine (80%), norepinephrine (20%)	Sympathetic preganglionic neurons; stress	Addisonian crisis (medullary contribution minor)	Pheochromocytoma

🔑 Pearl: "Salt, Sugar, Sex, Adrenaline" = Zona Glomerulosa (aldosterone), Zona Fasciculata (cortisol), Zona Reticularis (androgens/sex steroids), Medulla (catecholamines). Mnemonic: "GFR — Going From Rim to core" → Glomerulosa-Fasciculata-Reticularis from outside to inside.

▼3.2 Cushing's Syndrome — Diagnosis & Treatment

Cause	%	ACTH	Key Features
Cushing's disease (pituitary ACTH adenoma)	70%	↑ (ACTH-dependent)	Bilateral adrenal hyperplasia; women > men; weight gain, HTN, DM, osteoporosis
Ectopic ACTH (SCLC, carcinoid, MTC)	10–15%	↑↑ (very high)	Rapid onset; hypokalemia; hyperpigmentation; weight loss; severe myopathy
Adrenal adenoma	10%	↓ (ACTH-independent)	Unilateral mass; contralateral atrophy; DHEAS suppressed
Adrenal carcinoma	5%	↓	Rapid progression; large mass (>4 cm); elevated DHEAS/androgens; virilization
Exogenous steroids	Most common overall	↓↓	Iatrogenic; check all steroid routes (inhaled, topical, intra-articular); low DHEAS

Diagnostic Approach (Endocrine Society 2022)

Step 1 — Confirm hypercortisolism (any 2 of 3 tests positive):

24h UFC (urine free cortisol) — 2 separate collections; >3× ULN = strong evidence; less reliable in CKD
Late-night salivary cortisol (LNSC) — 2 samples at 11 PM; >2× ULN; best sensitivity (90%)
1 mg overnight DST (low-dose dexamethasone suppression): cortisol <1.8 mcg/dL rules out Cushing's (sensitivity 95%); 2-day LDDST for confirmation

Step 2 — ACTH level: ACTH <5 pg/mL = ACTH-independent (adrenal); ACTH >15 = ACTH-dependent (pituitary or ectopic)

Step 3 — If ACTH-dependent: distinguish pituitary vs ectopic:

MRI pituitary (adenoma found in 60% of Cushing's disease cases)
High-dose DST (8 mg overnight or 2-day 2 mg q6h): suppression ≥50% → pituitary (Cushing's disease); no suppression → ectopic or adrenal
Inferior petrosal sinus sampling (IPSS): gold standard — central:peripheral ACTH ratio ≥2 (baseline) or ≥3 (CRH-stimulated) = pituitary; most reliable test when MRI negative

Treatment	Indication	Drug/Approach	Remission Rate
Transsphenoidal surgery (TSS)	Cushing's disease (1st line)	Endoscopic endonasal approach; experienced neurosurgeon	70–80% (initial); 15–20% recurrence
Repeat TSS / Radiotherapy	Recurrent/persistent Cushing's disease	Stereotactic radiosurgery (Gamma Knife); remission 50–60% at 2–3 years	50–60%
Bilateral adrenalectomy	Failed pituitary/ectopic treatment	Laparoscopic; permanent adrenal insufficiency; risk Nelson syndrome (↑ACTH, hyperpigmentation, pituitary tumor enlargement)	100% cortisol control
Pasireotide (Signifor) SC	Cushing's disease (medical)	SSA with high affinity for SST5; ↓ACTH; 300–900 mcg BID SC; high rate of hyperglycemia	20–30% UFC normalization
Cabergoline	Cushing's disease (medical)	D2 agonist; 0.5–7 mg/week; ↓ACTH from corticotrophs; modest efficacy	25–40%
Ketoconazole, Metyrapone, Mitotane	Steroidogenesis inhibitors (adrenal-directed)	Block cortisol synthesis; ketoconazole (11β-OHase); metyrapone (11β-OHase); osilodrostat (FDA 2020: selective 11β-OHase inhibitor)	Variable; 50–70% for osilodrostat
Mifepristone (Korlym)	Cushing's + T2DM/glucose intolerance	GR antagonist; ↓glucose but UFC remains ↑ (can't monitor UFC on mifepristone)	Clinical improvement in ~50%

▼3.3 Adrenal Insufficiency — Primary, Secondary, Tertiary

Type	Cause	ACTH	Aldosterone	Distinguishing Features
Primary AI (Addison's disease)	Autoimmune (70%), TB, adrenal hemorrhage (Waterhouse-Friderichsen — meningococcemia), metastases, adrenoleukodystrophy	↑↑	↓	Salt craving, hyperkalemia, hyponatremia, hyperpigmentation (ACTH/MSH crossreactivity)
Secondary AI	Pituitary disease (tumor, surgery, Sheehan's), exogenous steroids (most common)	↓ or inappropriately normal	Normal	No hyperpigmentation; no mineralocorticoid deficiency (aldosterone intact); may have other pituitary deficiencies
Tertiary AI	Hypothalamic disease; chronic exogenous steroid → CRH suppression	↓	Normal	Same as secondary; most common cause: chronic glucocorticoid use >3 weeks

Diagnosis:

AM cortisol (8 AM): <3 mcg/dL = AI highly likely; >18 = AI excluded; 3–18 = indeterminate → stimulation test
250 mcg ACTH stimulation test (Cosyntropin): Cortisol <18 mcg/dL at 30 or 60 min = AI. Note: may miss early secondary AI (adrenals not yet atrophied); 1 mcg low-dose test more sensitive for secondary.
Assess ACTH: ↑↑ = primary; ↓/normal = secondary/tertiary
Primary AI: check 21-hydroxylase antibodies, VLCFA (adrenoleukodystrophy in males), adrenal CT

Treatment:

Hydrocortisone 15–25 mg/day in 2–3 divided doses (higher AM dose; mimic diurnal rhythm) — preferred for primary AI
Fludrocortisone 0.05–0.2 mg daily — for primary AI only (mineralocorticoid replacement); target: normal BP, electrolytes, PRA in normal range
Sick day rules: double or triple hydrocortisone dose for febrile illness, injury; IM/IV hydrocortisone for vomiting/surgery
Medic-alert bracelet; emergency hydrocortisone injection kit (100 mg IM)

🔑 Adrenal Crisis: Life-threatening emergency. Precipitated by: infection, surgery, vomiting (unable to take oral steroids), trauma. Features: severe hypotension, vomiting, abdominal pain, fever, hyponatremia, hyperkalemia, hypoglycemia. Treatment: IV hydrocortisone 100 mg bolus → 200 mg/24h continuous infusion or 50 mg q6h IM/IV. Aggressive IV NS. Do NOT delay for cortisol levels. Mortality ~6% per crisis episode.

▼3.4 Primary Hyperaldosteronism — Endocrine Society 2024

Most common cause of secondary hypertension. Prevalence: 5–15% of hypertensive patients (previously thought rare). Caused by autonomous aldosterone hypersecretion independent of the renin-angiotensin system.

Subtype	Frequency	Laterality	Treatment
Bilateral adrenal hyperplasia (BAH) / Idiopathic hyperaldosteronism (IHA)	60–70%	Bilateral	Medical: MRA (spironolactone or eplerenone)
Aldosterone-producing adenoma (APA, Conn's adenoma)	30–40%	Unilateral	Surgical: laparoscopic adrenalectomy (cure in 35–60%)
Unilateral adrenal hyperplasia	<2%	Unilateral	Surgical
Familial hyperaldosteronism type 1 (glucocorticoid-remediable)	Rare	Bilateral	Low-dose dexamethasone (suppresses ACTH-driven aldosterone)

Diagnostic Algorithm (ES 2024)

Screening: ARR (aldosterone-to-renin ratio) ≥30 (ng/dL)/(ng/mL/h) AND aldosterone >15 ng/dL → positive screen. Test in: resistant HTN (≥3 drugs), hypokalemia, incidentaloma, age <40 with HTN, family history. Ensure: hold spironolactone ≥4 weeks, hold ACEi/ARB ≥2 weeks, correct K+.
Confirmatory test (one of four): Oral sodium loading (3 days, 24h UFC aldosterone ≥12 mcg/day); IV saline infusion test (2L NS over 4h, aldosterone >10 ng/dL); fludrocortisone suppression test; captopril challenge.
CT adrenals: After biochemical confirmation. CT: 35% false-negative for APAs; 25% show incidentaloma not responsible for excess. Do NOT use CT alone for lateralization.
Adrenal vein sampling (AVS): Gold standard for lateralization before surgery. Selectivity index (SI) ≥3 (with ACTH) confirms catheterization. Lateralization index (LI) ≥4 = unilateral.

Drug	Dose	Mechanism	Advantages	Side Effects
Spironolactone	25–100 mg daily	Non-selective MRA; blocks aldosterone and androgen receptors	Cheap; effective; also used in HFrEF, ascites	Gynecomastia, sexual dysfunction, menstrual irregularity (anti-androgenic)
Eplerenone	25–100 mg BID	Selective MRA; aldosterone receptor only	No anti-androgenic SE; preferred in males	Less effective than spironolactone; more expensive
Finerenone	10–20 mg daily	Nonsteroidal selective MRA	Used in CKD+DM (FIDELIO/FIGARO); heart-safe; no gynecomastia	Hyperkalemia; not yet standard for PHA

▼3.5 Pheochromocytoma & Paraganglioma (PPGL)

PPGLs are catecholamine-secreting tumors: pheochromocytomas arise from adrenal medulla; paragangliomas from extra-adrenal sympathetic/parasympathetic ganglia. Rule of 10s (classic, now outdated — revised): ~10% bilateral, 10% malignant, 10% extra-adrenal; 30–40% are hereditary (germline mutation).

Gene	Syndrome	Tumor Type	Malignancy Risk
SDHB	Hereditary PGL	Extra-adrenal PGL (abdominal, thoracic, head/neck)	HIGH (25–40%)
SDHD	Hereditary PGL	Head/neck PGL (carotid body, jugular); paternal imprinting	Low (malignant rare)
VHL	Von Hippel-Lindau	Bilateral adrenal PHEO; norepinephrine secreting; ± RCC, hemangioblastoma	Low
RET	MEN2A/MEN2B	Bilateral adrenal PHEO; epinephrine-secreting	Low
NF1	Neurofibromatosis type 1	Adrenal PHEO; usually benign	Low
MAX, TMEM127	Sporadic-like	Adrenal bilateral	Low-moderate

Clinical Presentation: Classic triad = episodic headache, palpitations, diaphoresis. Hypertension (paroxysmal in 50%; sustained in 50%). Panic attack mimicry. Pale (not flushing — unlike carcinoid). Hyperglycemia (catecholamines → insulin inhibition). Incidentaloma on CT.

Biochemical Diagnosis:

First-line: Plasma free metanephrines (sensitivity 97%) OR 24h urine fractionated metanephrines/catecholamines — preferred over catecholamines alone
Metanephrines = O-methylation products of catecholamines — secreted continuously by tumor (even between episodes)
False positives: tricyclics, levodopa, labetalol (cross-reacts with assay), clonidine withdrawal, stress, acetaminophen
Clonidine suppression test: if plasma NE remains elevated despite clonidine → PHEO (normal subjects suppress)

Imaging & Treatment: CT abdomen/pelvis first. MIBG scan (¹²³I-MIBG) for functional imaging, metastatic disease. ¹⁸F-FDOPA PET: best for head/neck PGL and SDH-mutant tumors. Surgery: laparoscopic adrenalectomy. Pre-operative α-blockade mandatory (14 days minimum): Phenoxybenzamine (non-competitive) 10 mg BID → titrate; OR Doxazosin/Prazosin (competitive α1-blocker). Add β-blocker ONLY AFTER α-blockade (prevent unopposed α if β-blocked first → hypertensive crisis). High-salt, high-fluid diet pre-op. Intraoperative: phentolamine or nicardipine for crises; norepinephrine post-op for rebound hypotension.

▼3.6 Adrenal Incidentaloma — ESE/ENSAT 2023 Guidelines

Feature	Benign Adenoma	Concerning (Malignant/Functional)
Size	<4 cm	≥4 cm (↑malignancy risk; >6 cm → adrenal carcinoma risk 25%)
Hounsfield Units (HU) pre-contrast	≤10 HU (lipid-rich)	>10 HU (lipid-poor — indeterminate); >20 HU → suspicious
Washout (contrast-enhanced CT)	APW ≥60%; RPW ≥40%	APW <60% → non-adenoma
Borders	Well-defined, round	Irregular margins, heterogeneous, calcifications → ACC
MRI signal	Signal dropout on out-of-phase (lipid-rich)	No dropout → not adenoma

Functional Evaluation (all adrenal incidentalomas):

1 mg overnight DST — screen for MACS (mild autonomous cortisol secretion, formerly subclinical Cushing's): cortisol >1.8 but <5 mcg/dL after 1 mg DST. MACS → associated with ↑cardiometabolic risk; treat comorbidities; consider adrenalectomy if large, bilateral, or progressive comorbidities.
Plasma free metanephrines — rule out PHEO (before any biopsy or surgery)
ARR if hypertensive or hypokalemic — rule out PHA
DHEAS + testosterone — if virilization signs (exclude ACC)

▼3.7 Congenital Adrenal Hyperplasia (CAH)

Enzyme Defect	%	Gene	Cortisol	Aldosterone	Androgens	BP	Key Clinical
21-hydroxylase deficiency	90–95%	CYP21A2	↓	↓ (salt-wasting) or normal (simple virilizing)	↑↑	↓ (salt-wasting) or normal	46XX virilization; salt-wasting crisis in neonates; 17-OHP elevated (diagnostic)
11β-hydroxylase deficiency	5–8%	CYP11B1	↓	↓	↑	↑ (DOC accumulates → mineralocorticoid)	Virilization + hypertension; 11-deoxycortisol elevated
17α-hydroxylase deficiency	Rare	CYP17A1	↓	↑ (DOC)	↓	↑	46XY = female phenotype; sexual infantilism; hypokalemia HTN; both sexes have no sex steroids
3β-HSD deficiency	Rare	HSD3B2	↓	↓	Variable	↓	Salt-wasting; both sexes incomplete virilization

Treatment of 21-hydroxylase CAH: Hydrocortisone (glucocorticoid replacement + suppress ACTH → ↓androgen excess); Fludrocortisone (mineralocorticoid for salt-wasting form); Monitor 17-OHP, androstenedione, growth velocity, bone age. Adult monitoring: ACTH, 17-OHP, androstenedione, testosterone. Abiraterone acetate (off-label) under investigation to reduce glucocorticoid requirement. Tildacerfont (CRF1 antagonist) Phase 3 trials — reduces ACTH without increasing glucocorticoid dose.

📚 Key References — Section 3

ES Guidelines — Cushing's Syndrome 2022. Pivonello R et al. Endocrine 2022.
ES Guidelines — Primary Hyperaldosteronism 2024. Funder JW et al. J Clin Endocrinol Metab 2024.
ESE/ENSAT — Adrenal Incidentaloma 2023. Fassnacht M et al. Eur J Endocrinol 2023.
ES Guidelines — Pheochromocytoma/Paraganglioma 2014. Lenders JW et al. J Clin Endocrinol Metab 2014;99:1915.
Osilodrostat (LINC 3/4). Pivonello R. Lancet Diabetes Endocrinol 2020;8:748.

4. Pituitary & Hypothalamic Disorders

The pituitary gland — the "master gland" — integrates hypothalamic signals to regulate peripheral endocrine axes. This section covers pituitary adenomas, acromegaly, prolactinoma, Cushing's disease, hypopituitarism, diabetes insipidus, and SIADH.

▼4.1 Pituitary Anatomy & Hormonal Axes

Axis	Hypothalamic Factor	Anterior Pituitary	Target	Feedback
HPA	CRH (+)	ACTH (corticotrophs)	Cortisol (adrenal)	Cortisol (-) → CRH, ACTH
HPT	TRH (+)	TSH (thyrotrophs)	T3/T4 (thyroid)	T3/T4 (-) → TRH, TSH
HPG	GnRH (pulsatile +)	LH/FSH (gonadotrophs)	Sex steroids (gonads)	Sex steroids (-) feedback
GH axis	GHRH (+), Somatostatin (-)	GH (somatotrophs)	IGF-1 (liver)	IGF-1 (-); GH also directly fed back
Prolactin	Dopamine (PIF, -) via tuberoinfundibular pathway; TRH (+)	Prolactin (lactotrophs)	Breast, gonads	Prolactin itself (short loop) + dopamine
Posterior pituitary	ADH (AVP) from SON; Oxytocin from PVN	—	Renal collecting duct (aquaporin-2)	Osmolality, volume

🔑 Pearl: Prolactin is the ONLY anterior pituitary hormone under tonic inhibitory control (dopamine). Therefore, anything interrupting the pituitary stalk (tumor, trauma, surgery) → ↑PRL (stalk effect); other hormones → ↓. This explains why craniopharyngiomas cause ↑PRL + hypopituitarism of other axes simultaneously.

▼4.2 Pituitary Adenomas — Classification & General Management

Type	% of Pituitary Adenomas	Hormone Excess	First-Line Treatment
Prolactinoma	40–50%	Prolactin	Dopamine agonist (cabergoline)
Non-functioning (NFPA)	25–30%	None (or gonadotropin subunits)	Surgery if symptomatic (mass effect)
Somatotroph (acromegaly)	15–20%	GH + IGF-1	Surgery; SSA if not cured
Corticotroph (Cushing's disease)	10–15%	ACTH	Transsphenoidal surgery
Thyrotroph (TSHoma)	<1%	TSH	Surgery; SSA

Classification by size: Microadenoma <10 mm; Macroadenoma ≥10 mm. Macroadenomas → mass effects: bitemporal hemianopia (compression of optic chiasm), headache, hypopituitarism (compression of normal pituitary), stalk compression → ↑PRL.

Visual field testing: Goldmann perimetry or Humphrey automated perimetry. Bitemporal hemianopia (superior quadrants first). Urgent surgery for acute visual loss or apoplexy with visual compromise.

▼4.3 Acromegaly — Diagnosis & Treatment

GH-secreting adenoma → IGF-1 excess → acral growth, organomegaly, metabolic complications. Insidious onset; average 10-year delay to diagnosis. Mortality: 2–3× general population if untreated (CV disease, sleep apnea, colorectal cancer).

Clinical Features: Acral enlargement (hands, feet — ring/shoe size change), coarsened facial features, prognathism, macroglossia, frontal bossing, carpal tunnel syndrome, arthropathy, sleep apnea (80%), hypertension (35%), DM/IGT (50%), cardiomyopathy, colonic polyps/cancer risk ↑.

Diagnosis:

IGF-1 (age/sex-adjusted) elevated — best initial screening test; reflects integrated GH secretion
GH nadir during 75g OGTT: normal <0.4 ng/mL (UltraSensitive GH assay); >1 ng/mL confirms acromegaly (GH paradoxically ↑ or fails to suppress after glucose in acromegaly)
MRI pituitary with gadolinium
Echocardiogram, colonoscopy, polysomnography at baseline

Treatment	Remission Criteria	Outcomes
Transsphenoidal surgery (TSS) — 1st line	IGF-1 normal; GH nadir <0.4 ng/mL on OGTT	Microadenoma: 80–90% cure; Macroadenoma: 40–60% cure
Octreotide LAR / Lanreotide Autogel (SSA)	IGF-1 normalization in 40–70%	↓GH 50–70%; tumor shrinkage in 30–50%; first-line if surgery declined or high surgical risk; also used as adjunct
Pegvisomant (GHR antagonist)	IGF-1 normalization 90%	Does NOT lower GH; does NOT shrink tumor; SC daily; liver transaminase monitoring; most effective at normalizing IGF-1
Cabergoline	IGF-1 normalization 30–35%	Modest efficacy; useful in mild disease or mixed GH/PRL adenoma; oral weekly
Stereotactic radiosurgery (SRS)	IGF-1 normalization over years	50–60% at 5 years; main risk: hypopituitarism (50% at 10 years); used for residual tumor after surgery

🔑 Pearl: Octreotide LAR and Lanreotide can be used as primary therapy (pre-surgical) for 3–6 months to shrink large adenomas, or as definitive therapy if patient refuses/high-risk surgery. Pasireotide LAR (multi-receptor SSA) → higher IGF-1 normalization (15–20% more) but causes significant hyperglycemia (worsens T2DM/causes new DM in 57%).

▼4.4 Prolactinoma — Medical & Surgical Management

Most common pituitary adenoma (40–50%). Causes: microadenoma (women — amenorrhea, galactorrhea); macroadenoma (men — sexual dysfunction, visual field defects).

PRL elevation — differential diagnosis:

Physiologic: pregnancy (↑10x), breastfeeding, stress, sleep, post-coital
Drugs: D2 antagonists — antipsychotics (haloperidol, risperidone), metoclopramide, domperidone; antidepressants (TCAs, venlafaxine); antihypertensives (methyldopa, verapamil); H2 blockers; opioids
Stalk compression (any macroadenoma, craniopharyngioma): typically PRL <100–150 ng/mL (moderate); true prolactinoma often >200 ng/mL for macroprolactinoma
Hypothyroidism (TRH stimulates PRL release)
CKD (decreased clearance)

Drug	Dose	PRL Normalization	Tumor Shrinkage	Notes
Cabergoline (Dostinex)	0.25–2 mg 1–2×/week	80–90%	70–80%	First-line; better tolerated; once or twice weekly; risk of impulse control disorders (gambling, hypersexuality)
Bromocriptine (Parlodel)	1.25–15 mg daily (divided)	70–80%	60–70%	Older agent; more SE (nausea, orthostasis); safe in pregnancy (dopamine agonist approved)

Surgery (transsphenoidal): Indicated for: DA intolerance/resistance; macroadenoma with severe visual loss; CSF leak from DA-induced shrinkage; preference for cure. Remission rate: microprolactinoma 80–90%; macroprolactinoma 30–50%.

Pregnancy and prolactinoma: Stop cabergoline at confirmed pregnancy (bromocriptine preferred if medication needed in pregnancy — longer safety data). Microprolactinoma: very low risk of symptomatic growth in pregnancy. Macroprolactinoma: ↑risk of growth → visual field monitoring q trimester; restart DA or surgery if visual deterioration.

▼4.5 Hypopituitarism & GH Deficiency in Adults

Order of hormone loss in progressive pituitary disease: GH (first, most sensitive) → LH/FSH → TSH → ACTH → PRL (last to be lost; PRL may paradoxically ↑ with stalk effect).

Deficiency	Symptoms	Diagnosis	Replacement
ACTH (secondary AI)	Fatigue, hypotension, hypoglycemia, hyponatremia (free water retention due to ↑ADH); NO hyperpigmentation, NO hyperkalemia	8 AM cortisol; 250 mcg ACTH stimulation; ITT (gold standard)	Hydrocortisone 15–25 mg/day; NO fludrocortisone needed
TSH (secondary hypothyroidism)	Same as primary hypothyroidism	fT4 low with inappropriately low TSH; replace cortisol FIRST (avoid precipitating adrenal crisis)	Levothyroxine; target fT4 mid-upper normal range; TSH unreliable for dose adjustment
LH/FSH (hypogonadotropic hypogonadism)	Males: ED, ↓libido, infertility, muscle loss, osteoporosis; Females: amenorrhea, infertility, hot flashes, osteoporosis	Low testosterone (males) or estrogen (females) + inappropriately low LH/FSH	Males: Testosterone replacement; pulsatile GnRH or gonadotropins for fertility. Females: HRT; gonadotropins for ovulation induction
GH (adult GHD)	↑fat mass (central), ↓muscle mass, ↓bone density, impaired QoL, dyslipidemia, ↑CV risk	GH stimulation testing (ITT: GH<3 mcg/L; GHRH-arginine; glucagon stimulation); IGF-1 alone unreliable	Recombinant GH (Somatropin): 0.2–0.4 mg/day SC; adjust by IGF-1; SE: fluid retention, arthralgias, carpal tunnel, ↑DM risk

🔑 Insulin Tolerance Test (ITT): Gold standard for GH and ACTH reserve. Insulin 0.1 U/kg IV → achieve glucose <40 mg/dL (documented symptomatic hypoglycemia). GH <3 mcg/L = GHD. Cortisol <18 mcg/dL = secondary AI. Contraindicated: seizure disorder, IHD, severe hypopituitarism, age >60. Perform only with trained personnel and IV glucose at bedside.

▼4.6 Diabetes Insipidus & SIADH

Parameter	Central DI	Nephrogenic DI	Primary Polydipsia	SIADH
Serum Na	↑ (hypernatremia) if untreated	↑ if untreated	↓ (dilutional)	↓ (hyponatremia)
Urine osmolality (basal)	<300 mOsm/kg	<300 mOsm/kg	<300 (may suppress ADH)	>100 mOsm/kg (concentrated despite hyponatremia)
Plasma ADH	↓ (ADH deficiency)	Normal/↑ (renal resistance)	↓ (suppressed by water excess)	↑ (inappropriately high)
Water deprivation test	Uosm fails to rise; responds to desmopressin (Uosm ↑>50%)	Uosm fails to rise; NO response to desmopressin	Uosm rises appropriately (>750)	—
Copeptin test	Copeptin <2.6 pmol/L after hypertonic saline	Copeptin ↑↑ (high ADH)	Copeptin >4.9 (normal rise)	—

SIADH Causes (SIADH = Euvolemic Hyponatremia): CNS disease (stroke, SAH, meningitis), pulmonary (SCLC — ectopic ADH, pneumonia), drugs (SSRIs, carbamazepine, cyclophosphamide, NSAIDs, thiazides, oxytocin), pain/nausea, post-operative, hypothyroidism, adrenal insufficiency (exclude first).

SIADH Diagnosis (SIADH Criteria): Uosm >100 mOsm/kg + Serum Osm <275 + Euvolemia + UNa >30 mEq/L + Normal renal/thyroid/adrenal function.

Treatment:

Mild/chronic SIADH: fluid restriction (1–1.5 L/day); treat underlying cause
Moderate/severe (Na <120 or symptomatic): 3% NaCl — target ↑Na by 1–2 mEq/L/h, maximum +6–8 mEq/L in first 24h (prevent osmotic demyelination syndrome = ODS/CPM)
Tolvaptan (V2R antagonist) — effective for SIADH; risk of overly rapid correction; max 30 days (hepatotoxicity); initiate in hospital only
Desmopressin (DDAVP) — central DI: intranasal 10–40 mcg/day or oral 0.1–0.4 mg TID; monitor Na, fluid intake

📚 Key References — Section 4

ES Guidelines — Acromegaly 2014. Katznelson L et al. J Clin Endocrinol Metab 2014;99:3933.
ES Guidelines — Hypopituitarism 2016. Fleseriu M et al. J Clin Endocrinol Metab 2016;101:3888.
ES Guidelines — Prolactinoma 2011. Melmed S et al. J Clin Endocrinol Metab 2011;96:273.
ES Clinical Practice Guidelines — Diabetes Insipidus 2023. Christ-Crain M et al. Nat Rev Endocrinol 2019;15:672.
HYPOPIT — Pituitary Society Consensus 2022. Fleseriu M. Pituitary 2023.

5. Calcium & Bone Metabolism

▼5.1 Calcium Homeostasis — PTH-Vitamin D Axis

Calcium regulation: Normal serum Ca = 8.5–10.5 mg/dL (ionized: 4.6–5.3 mg/dL). 45% protein-bound (albumin); 10% complexed; 45% ionized (active form). Corrected Ca = measured Ca + 0.8 × (4.0 – albumin g/dL).

Hormone	Low Ca Trigger	Actions	Vitamin D Interaction
PTH	↓ ionized Ca → ↑PTH	↑Renal Ca reabsorption (DCT); ↑bone resorption (osteoclast activation); ↑1α-hydroxylase → ↑1,25(OH)2D; ↓renal phosphate reabsorption (phosphaturia)	Stimulates 1,25D synthesis
1,25(OH)2D (Calcitriol)	Low Ca + ↑PTH → ↑synthesis	↑GI Ca absorption (TRPV5/6); ↑GI phosphate absorption; ↑bone resorption (with PTH)	Produced by 1α-hydroxylase in kidney (CYP27B1)
Calcitonin	↑Ca → ↑calcitonin (C cells)	↓Bone resorption (↓osteoclasts); ↑renal Ca excretion; transient effect	Minor interaction
FGF-23	Produced by osteocytes; ↑phosphate → ↑FGF-23	↓1α-hydroxylase → ↓1,25D; ↑renal phosphate excretion; ↑klotho-dependent actions	Antagonizes 1,25D synthesis

▼5.2 Primary Hyperparathyroidism

Cause	Frequency	PTH	Ca	Phosphate	Key Feature
Solitary adenoma	85%	↑ (inappropriate)	↑	↓	Sporadic; usually curable with surgery
Multigland disease (hyperplasia)	10–15%	↑↑	↑	↓	Associated with MEN1 (4-gland hyperplasia), MEN2A, HRPT2 mutation
Parathyroid carcinoma	<1%	↑↑ (very high)	↑↑ (>14 mg/dL)	↓	Palpable neck mass; HRPT2/CDC73 mutation; markedly elevated PTH

Indications for Parathyroidectomy (ES 2022 Guidelines):

Serum Ca >1 mg/dL above ULN (i.e., >11.5 mg/dL)
Osteoporosis: T-score ≤−2.5 at any site; or vertebral fracture by imaging
eGFR <60 mL/min/1.73m²
Age <50 years
24h urine Ca >400 mg/day with ↑stone risk (nephrolithiasis/nephrocalcinosis by imaging)
Patient preference or inability for surveillance

Preoperative localization: 4D-CT (best sensitivity 80–90%); sestamibi scan (²⁰¹Tl/⁹⁹mTc-MIBI); US neck; 18F-choline PET (emerging — superior for small adenomas). Intraoperative PTH monitoring: >50% drop from baseline at 10 min post-excision = cure (Miami criterion).

Medical management (non-surgical): Adequate hydration; avoid thiazides/lithium; bisphosphonates for bone protection; Cinacalcet (calcimimetic, Sensipar) 30–90 mg BID — ↓serum Ca but does NOT improve BMD; for those unfit for surgery.

▼5.3 Osteoporosis — AACE/ACE 2020 & ADA 2025 Framework

Diagnosis: DXA T-score ≤−2.5 (osteoporosis); −2.5 to −1.0 (osteopenia); ≥−1.0 (normal). FRAX score: 10-year major osteoporotic fracture risk. Treat if: T-score ≤−2.5; FRAX major ≥20% or hip ≥3%; or low-trauma fracture at age ≥50.

Drug	Class	MOA	Fracture Reduction	Duration/Notes
Alendronate 70 mg weekly / Risedronate 35 mg weekly	Bisphosphonate	Inhibit osteoclast farnesyl pyrophosphate synthase → osteoclast apoptosis	Vertebral ↓47–70%; Hip ↓40–51%	Holiday after 5 years (oral BP); assess at 5 years; beware atypical femur fracture, ONJ
Zoledronic acid (Reclast) 5 mg IV yearly	Bisphosphonate IV	Same; most potent BP	Vertebral ↓70%; Hip ↓41%; non-vertebral ↓25%	HORIZON trial; 3-year initial course; also prevents fractures post-hip fracture (NEJM 2007)
Denosumab (Prolia) 60 mg SC q6 months	RANK-L inhibitor	Blocks RANK-L → ↓osteoclast differentiation; continuous suppression	Vertebral ↓68%; Hip ↓40%	FREEDOM trial; can use in CKD; NO drug holiday — rebound vertebral fracture risk if discontinued without transition to BP; hypocalcemia risk
Teriparatide (Forteo) 20 mcg SC daily	PTH 1-34 (anabolic)	Stimulates osteoblast activity; net bone formation	Vertebral ↓65%; Non-vertebral ↓53%	Max 2 years (osteosarcoma risk in rodents; black box warning); use in severe osteoporosis; follow with antiresorptive
Abaloparatide (Tymlos) 80 mcg SC daily	PTHrP 1-34 analog (anabolic)	Preferential anabolic action; less PTH-like resorption	Vertebral ↓86%; Non-vertebral ↓43%	ACTIVE trial; 2-year max; transition to antiresorptive
Romosozumab (Evenity) 210 mg SC monthly × 12 months	Sclerostin inhibitor (dual action)	↑bone formation + ↓resorption simultaneously	Vertebral ↓73%; Hip ↓38%	ARCH, FRAME trials; 12-month course then antiresorptive; black box: CV events (MI, stroke) — avoid in recent MI/stroke
Raloxifene (Evista) 60 mg daily	SERM	Estrogen receptor agonist in bone; antagonist in breast	Vertebral ↓30–50%; NO hip benefit	↓breast cancer risk (MORE trial); ↑DVT; hot flashes; NOT in women with severe hot flashes

🏆 AACE 2020 Risk Stratification — Treatment Selection

High risk: T-score −2.5 to −3.0, FRAX major 20–30% or hip 3–4.5%, no prior fracture → Start bisphosphonate or denosumab
Very high risk: Prior hip/vertebral fracture, T-score <−3.0, FRAX major >30% or hip >4.5%, or fracture on BP therapy → Start anabolic (teriparatide, romosozumab, abaloparatide) FIRST, then antiresorptive ("sequence therapy")
Imminent fracture risk: Recent fracture (<2 years) → romosozumab for 12 months (if no CV contraindication), then zoledronate

▼5.4 Vitamin D Deficiency & Metabolic Bone Disease

25(OH)D Level	Status	Clinical Significance
<12 ng/mL	Severe deficiency	Osteomalacia/rickets; myopathy; secondary HPT; ↑PTH
12–20 ng/mL	Deficiency	↑Fracture risk; impaired Ca absorption
20–30 ng/mL	Insufficiency	Some extra-skeletal effects (controversial)
30–80 ng/mL	Adequate (ES target: ≥30)	Optimal bone and Ca homeostasis
>150 ng/mL	Toxicity	Hypercalcemia, hypercalciuria, nephrocalcinosis

Treatment: Vitamin D3 (cholecalciferol) preferred over D2 (ergocalciferol) — better bioavailability, longer half-life. Loading: 50,000 IU D2 or D3 weekly × 8–12 weeks for severe deficiency. Maintenance: 1,500–2,000 IU/day. Calcium: 1,000–1,200 mg/day (diet preferred; supplements if needed). Caution: granulomatous diseases (sarcoid, TB) — ↑1,25D extrarenally → supplement cautiously, monitor Ca.

📚 Key References — Section 5

ES Guidelines — Primary Hyperparathyroidism 2022. Bilezikian JP et al. J Clin Endocrinol Metab 2022;107:2933.
AACE/ACE — Osteoporosis Algorithm 2020. Camacho PM et al. Endocr Pract 2020;26(Suppl 1):1–67.
FREEDOM (Denosumab). Cummings SR et al. NEJM 2009;361:756–765.
ARCH (Romosozumab vs Alendronate). Saag KG et al. NEJM 2017;377:1417.
HORIZON (Zoledronic acid). Black DM et al. NEJM 2007;356:1809.
ES Guidelines — Vitamin D 2011 (updated 2024). Holick MF. J Clin Endocrinol Metab 2011;96:1911.

6. Lipid Disorders & Cardiovascular Risk

Dyslipidemia is a primary modifiable risk factor for ASCVD. This section integrates the ACC/AHA 2018/2023 Cholesterol Guidelines, ESC/EAS 2019/2023 Guidelines, and landmark lipid-lowering trials including FOURIER, ODYSSEY OUTCOMES, CLEAR Harmony, and ORION trials.

▼6.1 Lipoprotein Metabolism & Classification

Lipoprotein	Major Lipid	Apolipoproteins	Source	Atherogenicity
Chylomicrons	TG (85–88%)	ApoB-48, ApoC-II, ApoE	Intestine (dietary fat)	None (too large)
VLDL	TG (50–65%)	ApoB-100, ApoC-II, ApoE	Liver (endogenous TG)	Moderate (VLDL remnants)
IDL (remnant)	TG + Chol	ApoB-100, ApoE	VLDL lipolysis	High (IDL → LDL or cleared)
LDL	Chol (45–50%)	ApoB-100 only	IDL lipolysis; hepatic LDLR removes	Very High (direct plaque)
Lp(a)	LDL-like + apo(a)	ApoB-100 + Apo(a)	Liver; genetically determined	Very High (genetic risk; TG-lowering doesn't help)
HDL	Chol (20–30%)	ApoA-I, ApoA-II	Liver + intestine; reverse cholesterol transport	Protective (negative correlation)

▼6.2 ASCVD Risk Stratification & LDL Targets

Risk Category	Definition	LDL Target	Non-HDL Target
Very High Risk	Clinical ASCVD (MI, stroke, PAD, ACS) + either: multiple major ASCVD events OR major ASCVD event + multiple high-risk conditions (DM, HTN, CKD, smoking, LDL≥100 on max statin)	<55 mg/dL (ESC/EAS 2019); <70 mg/dL (ACC/AHA 2018)	<85 mg/dL
High Risk	Single major ASCVD event; or DM+1 risk factor; or FH; or eGFR<30; or ASCVD risk >20% 10y	<70 mg/dL (ESC); <70 mg/dL (AHA)	<100 mg/dL
Intermediate Risk	10-year ASCVD risk 7.5–19.9%	<100 mg/dL	<130 mg/dL
Low Risk	10-year ASCVD risk <7.5%	<116 mg/dL (ESC); lifestyle modification (AHA)	<145 mg/dL

🔑 Pearl: "Lower is better" — no J-curve for LDL. IMPROVE-IT (ezetimibe + statin): LDL 53 mg/dL → ↓MACE vs 69 mg/dL. FOURIER (evolocumab): LDL 30 mg/dL → continued benefit. No safety concern for LDL <20 mg/dL. ACC/AHA 2018: If on maximally-tolerated statin and LDL still ≥70 mg/dL with ASCVD → add ezetimibe, then PCSK9i.

▼6.3 Lipid-Lowering Pharmacotherapy

Drug Class	LDL ↓	MOA	Key Trials	Notable SE
High-intensity statins (Rosuvastatin 20–40 mg; Atorvastatin 40–80 mg)	50–55%	HMG-CoA reductase inhibition → ↑hepatic LDLR expression	4S, WOSCOPS, JUPITER, TNT, PROVE-IT	Myopathy (0.1–0.5%); rhabdomyolysis (rare); ↑DM (10% relative risk ↑); ↑LFT (rare)
Ezetimibe (Zetia) 10 mg daily	15–22%	Inhibits NPC1L1 in intestinal brush border → ↓cholesterol absorption	IMPROVE-IT 2015, NEJM (MACE ↓6.4% vs statin alone)	Well-tolerated; occasional GI symptoms; no myopathy
PCSK9 inhibitors: Evolocumab (Repatha) 140 mg q2w or 420 mg monthly; Alirocumab (Praluent) 75–150 mg q2w	50–60% (on top of statin)	Anti-PCSK9 mAb → ↑hepatic LDLR recycling → ↓LDL clearance	FOURIER 2017 (Evolocumab, NEJM): MACE ↓15%; CV death NS; ODYSSEY OUTCOMES 2018 (Alirocumab): MACE ↓15%; all-cause mortality ↓15% (NNT=100)	Injection site reactions; myalgia (rare); extremely well-tolerated; expensive ($5,000–14,000/year)
Inclisiran (Leqvio) 284 mg SC q6 months after initial 2 doses	50% (sustained)	siRNA targeting PCSK9 mRNA in hepatocytes → ↓PCSK9 synthesis	ORION-10 & ORION-11 (2020, NEJM): LDL ↓50%; CVOT ongoing (ORION-4)	Injection site reactions (rare); twice-yearly dosing → excellent adherence
Bempedoic acid (Nexletol) 180 mg daily	18–25%	Inhibits ACL (upstream of HMG-CoA reductase); prodrug activated in liver; NO muscle activation (not converted in muscle)	CLEAR Harmony 2023, NEJM: MACE ↓13% vs placebo in statin-intolerant; CV death NS	Hyperuricemia, gout ↑; tendon rupture (rare); no myopathy (key advantage for statin-intolerant)
Bile acid sequestrants: Cholestyramine, Colesevelam	15–18%	↓bile acid reabsorption → ↑bile synthesis from cholesterol → ↑hepatic LDLR	Classic agents; Colesevelam: ↓HbA1c ~0.5% in T2DM (bonus)	GI: constipation, bloating; interfere with drug absorption (separate by 4h)
Fibrates: Fenofibrate, Gemfibrozil	Minimal (may ↑LDL)	PPARα → ↑LPL → ↑TG clearance; ↑HDL; ↓TG 25–50%	ACCORD-Lipid (fenofibrate + simvastatin): no CV benefit; Gemfibrozil + statin → ↑myopathy risk	Myopathy (↑with statin); ↑Cr (benign, non-structural); avoid Gemfibrozil + statin
Omega-3 FA: Icosapentaenoic acid (IPE, Vascepa) 4g daily	Minimal	TG ↓20–30%; unclear CV mechanism (may be pleiotropic)	REDUCE-IT 2018, NEJM: MACE ↓25% vs mineral oil placebo; controversy about control arm (mineral oil ↑CRP)	AF ↑ (small); fishy burping; bleeding (high dose)

🏆 Familial Hypercholesterolemia (FH)

Heterozygous FH: LDLR, ApoB, PCSK9 mutations; LDL 190–400 mg/dL; tendon xanthomas; arcus cornealis; premature ASCVD; 1:250 prevalence (most common monogenic disorder)
Homozygous FH: LDL >400 mg/dL; cutaneous xanthomas (childhood); untreated MI before age 20; 1:300,000
Dutch Lipid Clinic Network Criteria for FH diagnosis: family history, clinical signs, LDL level, genetic confirmation
Treatment FH: Max-intensity statin + ezetimibe + PCSK9i. HoFH: Add Lomitapide (MTP inhibitor) or Evinacumab (ANGPTL3 inhibitor, FDA 2021)
Cascade screening: screen all first-degree relatives of FH probands (DNA or lipid-based)

📚 Key References — Section 6

ACC/AHA Cholesterol Guidelines 2018. Grundy SM et al. J Am Coll Cardiol 2019;73:3168.
ESC/EAS Dyslipidemia Guidelines 2019. Mach F et al. Eur Heart J 2020;41:111.
FOURIER (Evolocumab). Sabatine MS et al. NEJM 2017;376:1713.
ODYSSEY OUTCOMES (Alirocumab). Schwartz GG et al. NEJM 2018;379:2097.
IMPROVE-IT (Ezetimibe). Cannon CP et al. NEJM 2015;372:2387.
CLEAR Harmony (Bempedoic acid). Nissen SE et al. NEJM 2023;388:1353.
REDUCE-IT (Icosapentaenoic acid). Bhatt DL et al. NEJM 2019;380:11.

7. Obesity & Metabolic Syndrome

▼7.1 Obesity — Classification & Pathophysiology

Class	BMI (kg/m²)	Asian BMI Cut-off	Metabolic Risk
Underweight	<18.5	<18.5	—
Normal	18.5–24.9	18.5–22.9	Average
Overweight	25–29.9	23–27.4	Mildly ↑
Obesity Class I	30–34.9	27.5–32.4	Moderately ↑
Obesity Class II	35–39.9	32.5–37.4	Severely ↑
Obesity Class III (Severe)	≥40	≥37.5	Very severely ↑

Pathophysiology: Leptin resistance (hypothalamic) → impaired satiety signaling; ghrelin (hunger hormone from stomach) → unaffected by fat mass; ↑adipose-derived adipokines (TNF-α, IL-6, resistin) → systemic inflammation and insulin resistance; visceral adiposity (waist circumference) more metabolically harmful than subcutaneous fat.

▼7.2 Metabolic Syndrome — IDF/AHA/NHLBI Harmonized Criteria 2009

Metabolic syndrome: ≥3 of 5 criteria → 5× ↑T2DM risk; 2–3× ↑CVD risk:

Component	Cut-off (General)	Asian Cut-off (Waist)
Waist circumference (abdominal obesity)	≥102 cm (M), ≥88 cm (F)	≥90 cm (M), ≥80 cm (F) [WHO Asian; also used in Thailand]
Triglycerides	≥150 mg/dL (or on TG-lowering therapy)	Same
HDL cholesterol	<40 mg/dL (M), <50 mg/dL (F)	Same
Blood pressure	≥130/85 mmHg (or on antihypertensive)	Same
Fasting glucose	≥100 mg/dL (or on glucose-lowering therapy)	Same

▼7.3 Anti-Obesity Pharmacotherapy — 2024 Updates

Drug	MOA	Weight Loss (1 year)	Key Trial	Contraindications/SE
Semaglutide 2.4 mg (Wegovy) SC weekly	GLP-1 RA — ↓appetite, ↓gastric emptying, ↑satiety	−15–17% body weight	STEP 1, NEJM 2021: −14.9 kg vs −2.4 kg placebo; SELECT 2023: MACE ↓20%	MTC/MEN2 CI; nausea/vomiting; gastroparesis; titrate slowly
Tirzepatide 10–15 mg (Zepbound) SC weekly	GIP + GLP-1 dual agonist	−20–22% body weight	SURMOUNT-1, NEJM 2022: −20.9 kg (15 mg) vs −3.1 kg placebo; SURMOUNT-MMO: MACE ongoing	Same as GLP-1 RA; MTC/MEN2 CI; superior weight loss to semaglutide (head-to-head: SURMOUNT-5, 2025)
Naltrexone/Bupropion ER (Contrave)	Opioid antagonist + DA/NE reuptake inhibitor → ↓food reward	−5–6%	COR-I, COR-II, COR-BMOD trials	CI: uncontrolled HTN, seizure disorder, opioid use, MAOIs; ↑BP initially
Phentermine/Topiramate ER (Qsymia)	Sympathomimetic + anticonvulsant/carbonic anhydrase inhibitor	−8–10%	EQUIP, CONQUER trials	CI: pregnancy (topiramate teratogenic — cleft palate); glaucoma; MAOIs; cognitive SE; taste changes
Orlistat (Xenical/Alli) 120 mg TID with meals	GI lipase inhibitor → ↓fat absorption (~30%)	−3–4%	XENDOS trial (orlistat + lifestyle vs lifestyle alone)	Oily spotting, steatorrhea, fat-soluble vitamin malabsorption; take vitamins 2h before or after

🔑 Retatrutide (Phase 3, 2024): Triple agonist (GIP + GLP-1 + glucagon receptors). NEJM 2023: 48-week weight loss up to −24.2% body weight — unprecedented for a pharmacological agent. Expected FDA review 2025–2026. Glucagon component further ↑energy expenditure (thermogenesis) and ↓liver fat.

▼7.4 Bariatric Surgery — Procedures & Metabolic Outcomes

Procedure	Weight Loss (%EWL)	T2DM Remission	Mechanism	Complications
Roux-en-Y Gastric Bypass (RYGB)	70–80%	60–80%	Restriction + malabsorption + hormonal (↑GLP-1, PYY; ↓ghrelin)	Dumping syndrome; nutritional deficiencies (Fe, B12, Ca, folate, thiamine); marginal ulcer; internal hernia
Sleeve Gastrectomy (SG)	60–70%	50–65%	Restriction + ↓ghrelin (gastric fundus removed) + ↑GLP-1	GERD (worsens in ~20%); stricture; leak; vitamin deficiencies (less than RYGB)
Adjustable Gastric Banding (AGB)	45–55%	40–50%	Restriction only	Band slippage, erosion, port issues; lowest complication rate; highest reoperation rate; declining use
Biliopancreatic Diversion + DS (BPD/DS)	80–90%	90–95%	Malabsorption dominant; severe fat malabsorption	Severe malnutrition; protein malabsorption; vitamin deficiencies; only for severe obesity

Indications (NIH Criteria, updated 2022): BMI ≥40 OR BMI ≥35 + obesity-related comorbidity (DM, HTN, sleep apnea, NAFLD). New ASMBS/IFSO 2022: BMI ≥30 with DM or metabolic syndrome now eligible. Post-op: lifetime supplementation (multivitamin, calcium, B12, iron); annual monitoring.

📚 Key References — Section 7

STEP 1 (Semaglutide 2.4 mg). Wilding JP et al. NEJM 2021;384:989–1002.
SURMOUNT-1 (Tirzepatide). Jastreboff AM et al. NEJM 2022;387:205–216.
SELECT (Semaglutide CV outcomes, overweight). Lincoff AM et al. NEJM 2023;389:2221.
SURMOUNT-5 (Tirzepatide vs Semaglutide head-to-head). Aronne LJ et al. NEJM 2025.
ASMBS/IFSO Bariatric Indications Update 2022. Eisenberg D et al. Surg Obes Relat Dis 2022;18:1345.

8. Reproductive Endocrinology

▼8.1 PCOS — Rotterdam 2023 Criteria & Management

PCOS is the most common endocrine disorder in women of reproductive age (prevalence 8–13%). Heterogeneous: not all have polycystic ovaries; not all are hyperandrogenic.

Rotterdam Criteria (2003, reaffirmed 2023 International Evidence-Based Guideline): ≥2 of 3:

Oligo-ovulation or anovulation (irregular cycles <21 or >35 days)
Clinical or biochemical hyperandrogenism (hirsutism, acne, alopecia; ↑free testosterone, DHEAS)
Polycystic ovarian morphology on US (≥20 follicles per ovary OR ovarian volume >10 mL on either ovary — updated 2023 threshold)
After exclusion of: CAH (17-OHP), Cushing's, thyroid disease, hyperprolactinemia, androgen-secreting tumor

Phenotype	Features	Metabolic Risk
A (classic)	HA + OA + PCOM	Highest
B	HA + OA (no PCOM)	High
C	HA + PCOM (ovulatory)	Moderate
D (normoandrogenic)	OA + PCOM (no HA)	Lower

Goal	Treatment	Notes
Irregular cycles / Endometrial protection	Combined OCP (1st line); Progestin cycling (14 days/month if OCP CI)	Prevents endometrial hyperplasia from unopposed estrogen (anovulation)
Hirsutism	OCP + antiandrogen: Spironolactone 50–200 mg/day; Cyproterone acetate (not in US); Flutamide (hepatotoxic)	Finasteride (5α-reductase inhibitor) — teratogenic; use with contraception
Insulin resistance / Metabolic	Metformin (1st line if metabolic PCOS or IGT); lifestyle (5–10% weight loss → restore ovulation in 50%)	Inositol supplements (myo-inositol) — emerging evidence; improves IR and ovulatory function
Infertility / Ovulation induction	Letrozole (aromatase inhibitor, preferred over clomiphene — NEJM 2014 Legro: ↑live birth rate); Clomiphene; Gonadotropins; IVF	Letrozole 2.5–7.5 mg days 3–7; live birth rate 27.5% vs 19.1% clomiphene

🔑 Pearl: All women with PCOS should be screened for: glucose (OGTT preferred over FPG), lipid profile, BP, depression/anxiety, OSA (Epworth), BMI/waist circumference. PCOS doubles lifetime T2DM risk; quadruples risk of gestational DM. GLP-1 RA emerging for PCOS with obesity — ↓weight, ↓androgens, ↑ovulation rate.

▼8.2 Male Hypogonadism — Primary & Secondary

Type	Testosterone	LH/FSH	Cause	Treatment
Primary (hypergonadotropic)	↓	↑↑	Klinefelter's (47,XXY — most common; small testes, gynecomastia, infertility, ↑tall); orchitis; chemotherapy; cryptorchidism; trauma	Testosterone replacement (fertility not possible with primary testicular failure — use donor)
Secondary (hypogonadotropic)	↓	↓ or inappropriately normal	Pituitary/hypothalamic: hyperprolactinemia, pituitary tumor, Kallmann syndrome (anosmia + HH), hemochromatosis, obesity, opioids, anabolic steroids, chronic illness	Treat cause; GnRH pump or gonadotropins (hCG + FSH) for fertility; testosterone replacement if fertility not desired

Testosterone Replacement Therapy (TRT):

Formulations: Transdermal gel (daily; avoid skin transfer); IM testosterone cypionate/enanthate 200 mg q2w; testosterone undecanoate (Aveed) 750 mg IM q10 weeks (less frequent); patches (daily; local irritation).
Monitor: Testosterone level (mid-cycle for IM; 2–4h post-application for gel); hematocrit (target <54% — erythrocytosis risk); PSA (annual after age 40); bone density.
Contraindications: Prostate cancer; severe BPH with obstruction; erythrocytosis (>54%); untreated severe OSA; planned fertility (exogenous testosterone suppresses spermatogenesis).
Infertility with secondary hypogonadism: hCG 2,000 IU IM 3× weekly (stimulates LH receptor) ± FSH → restores spermatogenesis. DO NOT use testosterone if fertility desired.

▼8.3 Menopause & Hormone Therapy — NAMS 2022

Diagnosis: Menopause = 12 months amenorrhea without other cause. Average age 51 years. Perimenopause: irregular cycles, vasomotor symptoms; FSH ↑. Premature ovarian insufficiency (POI): menopause <40 years; FSH >25 on 2 occasions ≥4 weeks apart.

Indication	MHT Type	Benefits	Risks
Vasomotor symptoms (hot flashes, night sweats)	Combined EPT (if uterus intact): E + Progestogen; ET alone (if no uterus)	Most effective treatment; ↑QoL; ↑sleep; ↓GSM	Breast cancer (small ↑ with EPT, not ET alone per WHI); DVT/PE (oral estrogen); stroke (oral estrogen — low dose transdermal safer)
Bone protection	ET or EPT	↓Fracture risk (WHI); alternative to bisphosphonates in <60 yrs	Same as above
Genitourinary syndrome of menopause (GSM)	Local vaginal estrogen (ring, cream, tablet) — minimal systemic absorption	↑Vaginal moisture; ↓dyspareunia; ↓UTI recurrence	Minimal; can use without systemic risks; even in breast cancer survivors (controversial)

WHI Reanalysis (2019–2022 perspectives): Original WHI (2002) overestimated risks — older women (avg 63 years); CEE+MPA; oral route; no consideration of timing. "Timing hypothesis": MHT started <10 years of menopause or <60 years → CV neutral to beneficial; started >10 years → ↑CV events. NAMS 2022: MHT appropriate for healthy women <60 or within 10 years of menopause for symptom relief.

Alternatives to MHT for vasomotor symptoms: SSRIs/SNRIs (paroxetine, venlafaxine — FDA-approved for VMS); Clonidine; Gabapentin; Fezolinetant (NK3R antagonist, FDA 2023 — first non-hormonal FDA-approved VMS treatment; blocks hypothalamic thermoregulation).

📚 Key References — Section 8

International PCOS Evidence-Based Guideline 2023. Teede HJ et al. Hum Reprod Open 2023;hoad025.
Letrozole vs Clomiphene (PCOS fertility). Legro RS et al. NEJM 2014;371:119.
NAMS — MHT Position Statement 2022. Menopause 2022;29:767–794.
ES Guidelines — Testosterone Deficiency 2018. Bhasin S et al. J Clin Endocrinol Metab 2018;103:1715.
Fezolinetant (SKYLIGHT 1 & 2). Lederman S et al. NEJM 2023;389:1637.

9. Multiple Endocrine Neoplasia & Neuroendocrine Tumors

▼9.1 MEN1 — Werner Syndrome

MEN1: Autosomal dominant; MEN1 gene (tumor suppressor, chromosome 11q13); penetrance ~95% by age 50. Classic triad: Primary HPT (95%), Pituitary adenoma (30–40%), Pancreatic/duodenal NETs (30–80%).

Tumor Type	Frequency in MEN1	Functional Syndrome	Management
Primary HPT (4-gland hyperplasia)	95%	Hypercalcemia	3.5-gland parathyroidectomy or total parathyroidectomy + autotransplant; subtotal preferred; high recurrence
Gastrinoma (Zollinger-Ellison syndrome)	40–50%	Severe peptic ulcer disease, diarrhea, ↑fasting gastrin (>1000), ↑basal gastric acid	High-dose PPI; surgical resection if solitary; somatostatin analog; secretin stimulation test (diagnostic: gastrin ↑>200 after secretin)
Insulinoma	10–15%	Whipple's triad: hypoglycemia symptoms + glucose <55 + relief with glucose; C-peptide + proinsulin ↑ (endogenous)	Surgical enucleation; diazoxide (inhibits insulin secretion) temporarily; Everolimus (mTOR inhibitor); Lanreotide
VIPoma	Rare	WDHA syndrome (watery diarrhea, hypokalemia, achlorhydria); VIP >200 pg/mL	Octreotide; surgery
Glucagonoma	Rare	4 D's: Dermatitis (necrolytic migratory erythema, pathognomonic), Diabetes, DVT, Depression; glucagon >500 pg/mL	Surgery; SSA (octreotide); LMWH (DVT prophylaxis)
Pituitary adenomas (MEN1)	30–40%	Prolactinoma most common; GH (acromegaly); NFPA; Cushing's disease	Same as sporadic pituitary adenomas; larger and more aggressive than sporadic

Screening in confirmed MEN1 germline carriers: Annual: serum Ca + PTH, fasting glucose, insulin, proinsulin, gastrin, glucagon, VIP, chromogranin A; prolactin + IGF-1. MRI pituitary every 3–5 years. CT/MRI pancreas every 1–3 years. Thymic/pulmonary carcinoid — CT chest every 1–2 years.

▼9.2 MEN2A, MEN2B & Familial MTC

Syndrome	Gene/Codon	Components	Prophylactic Thyroidectomy Age
MEN2A (Sipple syndrome)	RET codon 634 (most common)	MTC (virtually 100%) + PHEO (50%) + Primary HPT (20–30%)	Codon 634: before age 5 years (high-risk category)
MEN2B	RET codon 918 (highest risk)	MTC (earliest onset, most aggressive) + PHEO (50%) + Marfanoid habitus + Mucosal neuromas (lips, tongue, conjunctiva) + Intestinal ganglioneuromatosis; NO HPT	Codon 918: within 6 months of life (very high-risk)
Familial MTC (FMTC)	Multiple RET codons (609, 768, 804, 891)	MTC only (no other MEN2 features); least aggressive	Moderate-risk: calcitonin-guided or age-based per codon

Management sequence in MEN2: Rule out PHEO first (before thyroid surgery — pre-op α-blockade for 14 days); then thyroid surgery; then address HPT (if bilateral adrenalectomy needed in MEN2A, address after thyroid). MTC surveillance post-thyroidectomy: calcitonin + CEA + neck US every 6 months × 2 years, then annually.

Targeted therapy for advanced MTC: Vandetanib (ZETA trial, Lancet 2012 — PFS ↑); Cabozantinib (EXAM trial — PFS ↑); both are multitargeted TKIs (RET, VEGFR, EGFR); RET-selective inhibitors: Selpercatinib (LIBRETTO-001) and Pralsetinib — superior selectivity, fewer SE, durable responses in RET-mutant MTC.

▼9.3 Gastroenteropancreatic NETs (GEP-NETs) & Carcinoid

Classification (WHO 2022)	Ki-67	Mitoses	Behavior	Prognosis
NET G1 (well-differentiated)	<3%	<2/10 HPF	Slow-growing; functional or non-functional	5-yr survival ~90%
NET G2	3–20%	2–20/10 HPF	Intermediate	5-yr survival ~60–80%
NET G3 (well-diff, high Ki-67)	>20%	>20/10 HPF	Aggressive but well-differentiated architecture	5-yr survival ~30%
NEC (poorly diff) — small or large cell	>55%	>20/10 HPF	Highly aggressive; similar to SCLC	5-yr survival <10%

Carcinoid Syndrome: Requires hepatic metastases (or extra-hepatic — serotonin not cleared by liver). Symptoms: episodic flushing (serotonin/histamine/bradykinin), watery diarrhea, bronchoconstriction, right-sided heart disease (carcinoid heart disease — tricuspid regurgitation, pulmonic stenosis — serotonin-induced fibrous plaques). Diagnosis: 24h urine 5-HIAA (serotonin metabolite). Chromogranin A: general NET marker.

Imaging: ⁶⁸Ga-DOTATATE PET-CT (Netspot) — gold standard for somatostatin receptor (SSTR2+) NETs; sensitivity ~97%; superior to OctreoScan (¹¹¹In-DTPA-octreotide).

Treatment:

Surgery: curative for localized; debulking for advanced functional NET
Octreotide LAR / Lanreotide: anti-proliferative (PROMID, CLARINET trials) + symptom control; first-line for progressive G1/G2 NET
Everolimus (mTOR inhibitor): RADIANT-3 (pancreatic NET, NEJM 2011: PFS ↑ 6.4 months); RADIANT-4 (non-functional GI/lung NET)
Sunitinib (TKI): pancreatic NET; PFS benefit (NEJM 2011)
PRRT (Peptide Receptor Radionuclide Therapy): ¹⁷⁷Lu-DOTATATE (Lutathera) — NETTER-1 trial (NEJM 2017): midgut NET, SSTR2+ → PFS ↑ 28 months vs octreotide HD; inpatient therapy; renal protection with amino acid infusion
Chemotherapy: NEC → platinum-based (cisplatin/carboplatin + etoposide); Streptozocin + 5-FU for pancreatic NET (older regimen)

📚 Key References — Section 9

ES Guidelines — MEN1 2012. Thakker RV et al. J Clin Endocrinol Metab 2012;97:2990.
ATA MEN2 Guidelines 2015. Wells SA et al. Thyroid 2015;25:567.
NETTER-1 (¹⁷⁷Lu-DOTATATE). Strosberg J et al. NEJM 2017;376:125.
CLARINET (Lanreotide). Caplin ME et al. NEJM 2014;371:224.
RADIANT-3 (Everolimus). Yao JC et al. NEJM 2011;364:514.
Selpercatinib (LIBRETTO-001). Wirth LJ et al. NEJM 2020;383:825.

10. Endocrine Emergencies

Endocrine emergencies are potentially fatal and require immediate recognition and treatment. This section covers DKA, HHS, severe hypoglycemia, thyroid storm, myxedema coma, adrenal crisis, and hypercalcemic crisis.

▼10.1 Diabetic Ketoacidosis (DKA) — ADA 2024 Protocol

Severity	Glucose	pH	Bicarb	Anion Gap	Ketones	Mental Status
Mild DKA	>250 mg/dL	7.25–7.30	15–18	>10	3+ urine; positive serum	Alert
Moderate DKA	>250 mg/dL	7.00–7.24	10–14	>12	3+ urine; positive serum	Alert/drowsy
Severe DKA	>250 mg/dL	<7.00	<10	>12	3+ urine; positive serum	Stupor/coma

Euglycemic DKA (euDKA): pH <7.3 + ketones + glucose <250 mg/dL. Occurs with: SGLT2i use (↑urinary glucose → normal glucose despite DKA), partial insulin therapy, pregnancy, alcohol. High index of suspicion needed.

ADA 2024 DKA Treatment Protocol

1. IV Fluids (first 1–2 hours): 0.9% NaCl 1–1.5 L/h for first 30 min, then 250–500 mL/h until euvolemic. Switch to 0.45% NaCl if corrected Na normal/high. When glucose reaches 200–250 mg/dL → change to D5W 0.45% NaCl to prevent hypoglycemia while continuing insulin to clear ketones.

2. Insulin: Do NOT start insulin until K+ ≥3.5 mEq/L (insulin drives K+ intracellularly → fatal hypokalemia). Regular insulin infusion 0.1 U/kg/h (or 0.14 U/kg/h without bolus). Target glucose decrease: 50–75 mg/dL/hour. When glucose 200–250 → reduce insulin to 0.05 U/kg/h + add dextrose.

3. Potassium replacement: K+ 3.5–5.0 → add 20–40 mEq/L to IV fluids; K+ <3.5 → replace aggressively before starting insulin; K+ >5.0 → hold K+ but monitor closely (acidosis correction → K+ drops). Target K+ 4–5 mEq/L.

4. Bicarbonate: Only for severe acidosis pH <6.9 (100 mEq NaHCO3 in 400 mL water over 2h). Routine bicarb use NOT recommended (↑cerebral edema risk; delays ketone clearance paradoxically in CNS).

5. Phosphate: Replace only if <1 mg/dL or symptomatic (respiratory failure, hemolytic anemia, cardiac dysfunction).

Resolution criteria: Glucose <200 + anion gap ≤12 + serum bicarb ≥15 + pH >7.3 + β-OHB <0.6 mmol/L. Transition to SC insulin: give SC rapid-acting + long-acting 1–2 hours before stopping insulin infusion (overlap).

Precipitants of DKA (6 I's): Infection (50%), Insulin omission (25%), Initial presentation (15%), Infarction (MI/stroke), Iatrogenic (steroids, SGLT2i, antipsychotics), Intoxication.

🔑 Cerebral Edema (DKA complication): More common in pediatric DKA. Risk factors: too-rapid glucose correction, high-dose bicarb, delayed diagnosis. Symptoms: headache, sudden deterioration, Cushing's triad. Treatment: mannitol 0.5–1 g/kg IV or hypertonic saline; reduce fluid rate; elevate HOB 30°; CT head. Mortality 20–40%; permanent neurologic deficit in 10–25% of survivors.

▼10.2 Hyperosmolar Hyperglycemic State (HHS)

Feature	DKA	HHS
Glucose	>250 mg/dL	>600 mg/dL (typically 800–1200)
Ketones	Positive (β-OHB >3 mmol/L)	Absent/trace (residual insulin suppresses ketogenesis)
pH	<7.30	>7.30 (normal)
Bicarbonate	<18 mEq/L	>18 mEq/L (normal)
Effective osmolality	Variable (may be elevated)	>320 mOsm/kg (key diagnostic criterion)
Fluid deficit	3–6 L	8–12 L (severe dehydration)
Onset	Hours (24–48h)	Days–weeks
Mortality	0.5–5%	15–20% (older patients, severe)

HHS Treatment: Aggressive IV hydration (0.9% NaCl initially; switch to 0.45% NaCl when Na normalizing); conservative insulin (0.05 U/kg/h — avoid rapid glucose drop → cerebral edema); correct K+; address precipitant (infection, MI most common); monitor for thrombosis (↑viscosity → DVT/PE); consider prophylactic anticoagulation.

▼10.3 Thyroid Storm — Burch-Wartofsky Score

Thyroid storm = life-threatening decompensated thyrotoxicosis. Mortality 20–30% even with treatment. Precipitants: surgery, trauma, RAI therapy, infection, parturition.

Burch-Wartofsky Parameter	Score
Temperature: 37.2–37.7°C (4pts); 37.8–38.2°C (8pts); 38.3–38.7°C (12pts); 38.8–39.2°C (16pts); 39.3–39.9°C (20pts); ≥40°C (24pts)	4–24
CNS: Absent (0); Mild agitation (10); Moderate delirium/psychosis (20); Severe seizure/coma (30)	0–30
GI/hepatic: Absent (0); Moderate diarrhea/nausea (10); Severe jaundice (20)	0–20
HR: <100 (0); 100–109 (5); 110–119 (10); 120–129 (15); 130–139 (20); ≥140 (25)	0–25
CHF: Absent (0); Mild pedal edema (5); Moderate dyspnea/crackles (10); Pulmonary edema (15)	0–15
AF: Absent (0); Present (10)	0–10
Precipitating event: Absent (0); Present (10)	0–10

Score interpretation: ≥45 = thyroid storm (high probability); 25–44 = impending storm; <25 = unlikely thyroid storm.

Treatment — Sequential Steps (BLOCK and REPLACE)

Block synthesis: PTU 200–400 mg q4–6h PO/NG (preferred over MMI — also blocks T4→T3 conversion) OR MMI 20–40 mg q4–6h
Block T4→T3 conversion + thyroid hormone release: Lugol's iodine 5 drops q6h (or SSKI) — given 1 hour AFTER PTU (prevent iodine from being used for hormone synthesis); IV hydrocortisone 100 mg q8h (Wolff-Chaikoff + blocks T4→T3 + treats possible concurrent AI)
Block peripheral effects: Propranolol IV/PO (non-selective β-blocker → ↓HR, blocks T4→T3 conversion); Esmolol infusion if IV needed. Target HR <100.
Supportive: IV fluids, cooling blankets, acetaminophen (NOT aspirin — displaces T4 from TBG); treat underlying cause; ICU monitoring
Definitive: Emergency thyroidectomy if not improving within 24–48h; or plasmapheresis for hormone removal

🔑 Pearl — Iodine Timing: Always give thionamide FIRST (1 hour before iodine). If iodine given before thionamide → iodine is substrate for more hormone synthesis (Jod-Basedow phenomenon). The Wolff-Chaikoff effect (iodine suppresses thyroid) is only transient — thionamide must block organification first.

▼10.4 Myxedema Coma

Life-threatening decompensated hypothyroidism. Mortality 20–40%. Precipitants: cold exposure, infection, sedatives/narcotics, surgery, stroke. Classic presentation: Altered mental status + hypothermia + bradycardia + hyponatremia + hypoventilation + ↑TSH + ↓fT4.

Treatment (empirical — do NOT wait for lab confirmation):

IV LT4 (levothyroxine): Loading dose 200–400 mcg IV × 1 (or 4 mcg/kg), then 1.6 mcg/kg/day IV. Converts to T3 gradually.
IV LT3 (liothyronine): Some centers add LT3 10–20 mcg IV q8h for first 24–48h (faster T3 availability); associated with ↑cardiac arrhythmia risk — use with caution in CAD/elderly.
Hydrocortisone 100 mg IV q8h: Give before or simultaneously with thyroid hormone — risk of concurrent secondary AI (hypothalamic-pituitary disease); thyroid hormone alone may precipitate adrenal crisis by ↑cortisol metabolism.
Warm IV fluids; passive rewarming (NOT active → risk peripheral vasodilation + CV collapse); treat precipitant; ICU; intubation if severe hypoventilation.
Avoid: Sedatives, opioids (worsen hypoventilation); nephrotoxic drugs.

▼10.5 Adrenal Crisis

Adrenal Crisis: Acute cortisol deficiency → distributive shock. Features: severe hypotension unresponsive to fluids/vasopressors, hypoglycemia, hyponatremia, hyperkalemia (primary AI), fever, abdominal pain, vomiting, altered consciousness. Can be fatal within hours if untreated.

Treatment (Act FAST — do not wait for cortisol levels):

Hydrocortisone 100 mg IV bolus → then 200 mg/24h continuous infusion OR 50 mg IV/IM q6h
IV 0.9% NaCl 1 L in first hour (volume + Na resuscitation); D5NS if hypoglycemic
Identify and treat precipitant (infection most common → empiric antibiotics)
Do NOT use dexamethasone first if diagnosis uncertain (allows cortisol measurement) — but if Addison's known, hydrocortisone immediately
Transition to oral HC when clinically stable (double/triple dose for ongoing illness)
At high-dose HC (>50 mg/day), mineralocorticoid effect sufficient — fludrocortisone not needed until HC <50 mg/day

Prevention: Sick day rules; medic-alert identification; IM hydrocortisone emergency kit; patient/family education. Perioperative: HC 100 mg IM before major surgery → 50 mg q8h × 24–48h → taper to maintenance over 3 days.

▼10.6 Hypercalcemic Crisis

Hypercalcemic crisis: Calcium >14 mg/dL (or >12 with symptoms). Symptoms: "Bones, Stones, Groans, Psychic Moans" — bone pain, renal stones, constipation/nausea, neuropsychiatric (confusion, psychosis, coma).

Causes by frequency: Primary HPT (80% of outpatient hypercalcemia) and Malignancy (80% of inpatient hypercalcemia). Others: Sarcoid/granulomatous (↑calcitriol), Milk-alkali, Vitamin D toxicity, Thiazides, FHH (familial hypocalciuric hypercalcemia — benign; high Ca, low Ca/Cr ratio), Immobilization, MEN1/2.

Step	Treatment	Mechanism	Onset
1	IV 0.9% NaCl 200–300 mL/h (hydration) — MOST IMPORTANT FIRST STEP	Volume expansion → ↑GFR → ↑Ca excretion; corrects dehydration (hypercalcemia → nephrogenic DI → dehydration → ↑Ca)	Hours
2	Loop diuretics (furosemide) — ONLY after adequate hydration (NOT before); 40–80 mg IV to maintain UO 100–200 mL/h	↑renal Ca excretion; prevent fluid overload	Hours
3	Zoledronic acid 4 mg IV over 15 min (most potent) OR Pamidronate 60–90 mg IV over 2–4h	Bisphosphonate → ↓osteoclast-mediated bone resorption (main driver in malignancy)	24–72h; peak effect 3–5 days
4	Calcitonin 4–8 IU/kg IM/SC q6–12h	Fastest-acting agent; ↓bone resorption + ↑renal Ca excretion; tachyphylaxis in 24–48h (downregulates receptors)	2–6 hours
5	Steroids (Prednisone 40–60 mg/day or Hydrocortisone 200 mg/day IV) — for granulomatous disease, hematologic malignancy, Vitamin D toxicity	↓1α-hydroxylase activity; ↓calcitriol production; ↓GI Ca absorption	Days
6	Denosumab 120 mg SC (for bisphosphonate-refractory or CKD patients)	RANKL inhibitor → ↓osteoclast activity; effective even in renal failure (unlike bisphosphonates)	24–72h
7	Dialysis (hemodialysis with low-Ca dialysate)	For severe refractory hypercalcemia, renal failure, fluid overload	Rapid

🔑 Pearl — FHH vs Primary HPT: Familial Hypocalciuric Hypercalcemia (FHH): CASR mutation → high Ca set point → hypercalcemia but low urinary Ca/Cr ratio <0.01; PTH normal/slightly elevated; benign — no treatment needed; surgery NOT indicated. Primary HPT: Ca/Cr ratio usually >0.02. FHH misdiagnosed as primary HPT → unnecessary parathyroidectomy. Always check Ca/Cr ratio (24h urine Ca÷serum Ca × serum Cr÷urine Cr) before surgery.

📚 Key References — Section 10

ADA — DKA/HHS Management 2024. Kitabchi AE. Diabetes Care 2009;32:1335 (updated 2024 standards).
ATA — Thyroid Storm 2016. Ross DS et al. Thyroid 2016.
ES — Adrenal Crisis Prevention 2016. Rushworth RL et al. Endocrine Rev 2019;40:1000.
ES — Hypercalcemia of Malignancy 2023. Minisola S et al. J Clin Endocrinol Metab 2023.
NICE-SUGAR (Intensive glycemic control in ICU). Finfer S et al. NEJM 2009;360:1283.