Endocrine

Multiple endocrine neoplasia syndromes: MEN1, MEN2A, MEN2B

Clinical Overview and When to Suspect MEN Syndromes

— MEN1 (Wermer): parathyroid hyperplasia, pancreatic neuroendocrine tumors, pituitary adenomas ("3 Ps"). Caused by germline mutation in MEN1 on 11q13 (menin, tumor suppressor).

— MEN2A (Sipple): medullary thyroid carcinoma (MTC), pheochromocytoma, primary hyperparathyroidism. RET proto-oncogene mutation on 10q11.2.

— MEN2B: MTC (earliest, most aggressive), pheochromocytoma, mucosal neuromas, marfanoid habitus. RET codon 918 (M918T) mutation in >95%.

— Hypercalcemia with elevated PTH in a patient <40 or with family history → think MEN1 or MEN2A.

— Recurrent peptic ulcers, secretory diarrhea, hypoglycemia, or nephrolithiasis clustering in a family.

— Pheochromocytoma at young age, bilateral, or with family history of thyroid cancer.

— Any MTC patient — even apparently sporadic — must undergo germline RET testing.

— Pituitary macroadenoma in a young patient with concurrent kidney stones.

Multiple endocrine neoplasia (MEN) syndromes are autosomal dominant disorders predisposing to synchronous or metachronous tumors in two or more endocrine glands.

Three classic syndromes tested on Step 3:

When to suspect in adult ambulatory practice:

Genetic testing thresholds: offer germline testing to index cases meeting clinical criteria and to all first-degree relatives. Pre-test and post-test counseling are required.

Step 3 management: Once a proband is identified, cascade testing of first-degree relatives is the highest-yield intervention — prophylactic thyroidectomy in RET-positive children can be curative before MTC develops.

Board pearl: The "2-of-3" clinical rule defines MEN1: tumors in ≥2 of parathyroid, pancreas, pituitary. A single tumor plus a first-degree relative with MEN1 also qualifies. Recognizing the syndrome unlocks an entire surveillance and family-screening cascade that drives most Step 3 vignette decisions.

Presentation Patterns and Key History

— Primary hyperparathyroidism (95%) is usually the first manifestation, often by age 20–25 — multigland hyperplasia, not a single adenoma. Presents as nephrolithiasis, fatigue, osteoporosis, or asymptomatic hypercalcemia.

— Enteropancreatic NETs (40–70%): gastrinoma (most common functional, → Zollinger-Ellison: recurrent/refractory PUD, diarrhea, jejunal ulcers), insulinoma (Whipple triad: hypoglycemia + neuroglycopenic symptoms + relief with glucose), VIPoma (watery diarrhea, hypokalemia, achlorhydria), glucagonoma (necrolytic migratory erythema, diabetes), nonfunctional NETs.

— Pituitary adenoma (30–40%): prolactinoma most common (galactorrhea, amenorrhea, infertility, low libido); also GH (acromegaly) or ACTH (Cushing).

— Other: foregut carcinoids (thymic in men, bronchial in women), adrenal cortical tumors, lipomas, angiofibromas, collagenomas.

— MTC (>95%) typically presents in the 2nd–3rd decade as a thyroid nodule with elevated calcitonin; cervical lymphadenopathy common.

— Pheochromocytoma (~50%): episodic headache, palpitations, diaphoresis, hypertension; often bilateral and adrenal.

— Primary hyperparathyroidism (~25%): milder than MEN1, usually single-gland.

— Variants: cutaneous lichen amyloidosis (interscapular pruritus), Hirschsprung disease.

— MTC in infancy/early childhood — metastatic by age 10 if untreated.

— Mucosal neuromas of lips/tongue ("bumpy lips"), intestinal ganglioneuromatosis (chronic constipation, megacolon).

— Marfanoid habitus without lens dislocation or aortic root disease; high-arched palate, pes cavus.

— Pheochromocytoma in ~50%; hyperparathyroidism is absent.

MEN1 typical presentations (penetrance ~95% by age 50):

MEN2A presentations:

MEN2B presentations (most aggressive):

Key distinction: MEN2B = MTC + pheo + neuromas/marfanoid, NO hyperparathyroidism. MEN2A = MTC + pheo + parathyroid. Knowing which "P" is missing distinguishes the two syndromes on virtually every board stem.

Physical Exam Findings and Hemodynamic Assessment

— MEN2B: marfanoid body habitus (long thin limbs, arachnodactyly), but no ectopia lentis and no aortic root dilation — the key discriminator from Marfan syndrome. Look for "blubbery" everted lips with visible mucosal neuromas, neuromas on tongue/buccal mucosa, and high-arched palate.

— MEN1: cutaneous stigmata include multiple facial angiofibromas (often confused with tuberous sclerosis), truncal collagenomas, and lipomas.

— MEN2A: scapular/interscapular cutaneous lichen amyloidosis — pruritic, hyperpigmented patches.

— Measure BP supine and standing — paroxysmal hypertension with orthostasis is classic (catecholamine-induced volume contraction).

— Sustained hypertension is actually more common than paroxysms.

— Tachycardia, tremor, pallor (not flushing — flushing favors carcinoid).

— Never palpate the abdomen vigorously if pheo suspected — can precipitate hypertensive crisis.

General inspection clues:

Thyroid exam: palpable firm nodule in MTC, often in upper poles (parafollicular C-cell distribution). Assess for cervical lymphadenopathy (central and lateral compartments).

Hemodynamic assessment for pheochromocytoma (MEN2A/B):

Hyperparathyroidism findings: usually subtle — band keratopathy rare; assess for nephrolithiasis tenderness (CVA), proximal muscle weakness, depression.

Pituitary signs: bitemporal hemianopsia (confrontation visual fields + formal perimetry), cranial nerve III/IV/VI palsies if cavernous sinus invasion, acromegalic features (frontal bossing, prognathism, soft-tissue enlargement, ring/shoe size change), Cushingoid features.

Pediatric MEN2B exam: alacrima (absent tearing) in infancy, feeding difficulties, constipation from intestinal ganglioneuromatosis — these precede the MTC diagnosis.

Step 3 management: Any patient presenting with a thyroid nodule plus episodic hypertension must have pheochromocytoma excluded biochemically before any thyroid surgery — operating on an undiagnosed pheo precipitates fatal intraoperative hypertensive crisis. This sequencing question appears repeatedly.

Diagnostic Workup — Initial Labs, Imaging, and Biomarkers

— Calcium + ionized calcium + PTH: elevated calcium with inappropriately normal or high PTH confirms primary hyperparathyroidism.

— Fasting gastrin (off PPI for 1 week if safe) with gastric pH — gastrin >1000 pg/mL with pH <2 supports gastrinoma.

— Fasting glucose and insulin/proinsulin/C-peptide during symptomatic hypoglycemia for insulinoma.

— Chromogranin A, pancreatic polypeptide, glucagon, VIP for nonfunctional and other functional NETs.

— Prolactin, IGF-1; if symptoms suggest Cushing → 24-h urinary free cortisol or late-night salivary cortisol.

— Calcitonin (basal): elevated in MTC; stimulated calcitonin testing largely obsolete.

— CEA: complementary tumor marker for MTC; rising CEA with stable calcitonin suggests dedifferentiation.

— Plasma free metanephrines OR 24-h urinary fractionated metanephrines annually starting age 8 (MEN2B, high-risk RET) or 11 (MEN2A) — most sensitive test for pheochromocytoma.

— Calcium + PTH for MEN2A (not needed for MEN2B).

— Neck ultrasound for thyroid nodule (MTC: hypoechoic, microcalcifications) and parathyroid localization.

— Pituitary MRI with gadolinium if biochemical pituitary disease suspected.

— Pancreas/duodenum: MRI or contrast-enhanced CT; endoscopic ultrasound is most sensitive for small pancreatic NETs (<1 cm).

— Adrenal CT or MRI if metanephrines elevated — pheochromocytomas in MEN are typically adrenal and may be bilateral.

MEN1 initial biochemical screening (annual in known carriers, starting age 5):

MEN2 initial biochemical screening:

Initial imaging:

Functional imaging: ⁶⁸Ga-DOTATATE PET/CT has replaced octreotide scintigraphy for somatostatin-receptor-positive NETs; high sensitivity for primary and metastatic disease. ¹²³I-MIBG is alternative for pheo.

Board pearl: DOTATATE PET/CT is the modern standard for staging pancreatic NETs and detecting metastatic MTC/pheo. Older boards taught octreotide scan — current Step 3 expects DOTATATE as the answer.

Diagnostic Workup — Advanced and Confirmatory Studies

— MEN1 testing: sequence MEN1 gene; ~10% of clinical MEN1 patients are mutation-negative (phenocopies or undetected mutations) — clinical diagnosis still applies.

— RET testing for MEN2: identifies codon-specific mutations that stratify MTC risk:

– Highest risk (ATA-HST): codon 918 (M918T) → MEN2B → thyroidectomy within first year of life.

– High risk (ATA-H): codons 634, 883 → MEN2A → thyroidectomy by age 5.

– Moderate risk (ATA-MOD): other RET mutations → thyroidectomy when calcitonin rises or by age 5–10.

— Plasma free metanephrines (supine, 30-min rest) — highest sensitivity (~99%).

— Equivocal results → clonidine suppression test (no fall in metanephrines with pheo) or 24-h urinary metanephrines for specificity.

— Sestamibi-SPECT/CT + neck ultrasound; in MEN1, 4-gland hyperplasia means localization is less critical — operative strategy is bilateral exploration.

— 4D-CT for re-operative cases.

Germline genetic testing is the definitive confirmatory test:

Confirmatory biochemical testing for pheochromocytoma:

Hyperparathyroidism localization (preop):

Gastrinoma localization: secretin stimulation test (paradoxical rise in gastrin >120 pg/mL with secretin) confirms gastrinoma; EUS and DOTATATE for localization. Gastrinomas in MEN1 are typically duodenal, small, and multifocal.

Pituitary: dynamic testing — oral glucose suppression for GH (acromegaly: failure to suppress <1 ng/mL), dexamethasone suppression and IPSS for Cushing.

MTC staging: neck US + contrast CT of neck/chest/abdomen if calcitonin >400 pg/mL; bone scan and MRI liver/spine for advanced disease.

Key distinction: In MEN1 hyperparathyroidism, preoperative localization is less critical because all 4 glands are abnormal — surgery is subtotal (3.5-gland) parathyroidectomy or total parathyroidectomy with autotransplantation, not focused exploration. In sporadic PHPT a single adenoma is targeted.

Risk Stratification and First-Line Management Logic

— MEN1: pancreatic NETs (especially gastrinoma/nonfunctional with metastases) and thymic carcinoids are leading causes of death — surveillance drives outcomes.

— MEN2A/2B: MTC is the principal cause of death; pheochromocytoma is the principal cause of perioperative death — exclude pheo before any surgery.

1. Always rule out pheochromocytoma first in any MEN2 patient before thyroid, parathyroid, or other surgery.

2. Treat pheochromocytoma before MTC if both present.

3. Treat hyperparathyroidism before or at the time of thyroidectomy in MEN2A.

— ATA-HST (M918T, MEN2B): total thyroidectomy in first year of life, ideally <6 months; central neck dissection if calcitonin elevated or nodes >5 mm.

— ATA-H (codon 634, 883): thyroidectomy by age 5, earlier if calcitonin rises.

— ATA-MOD: thyroidectomy when calcitonin elevates or by school age based on shared decision-making with family.

— Calcium/PTH from age 8; prolactin/IGF-1 from age 5; gastrin from age 20; pancreatic imaging from age 10; pituitary MRI every 3 years from age 5; chest imaging every 1–2 years from age 15.

Management is organized around the highest-mortality tumor in each syndrome:

Sequencing principle (high-yield):

RET-based MTC risk stratification (ATA 2015) drives prophylactic thyroidectomy timing:

MEN1 surveillance start ages (annual biochemistry; imaging every 1–3 years):

Functional vs nonfunctional NETs: resect functional NETs and nonfunctional NETs >2 cm (some say >1 cm) due to metastatic risk; smaller nonfunctional NETs surveilled with EUS/MRI.

CCS pearl: In an MEN2 vignette with new thyroid nodule and hypertension, your CCS order set is: plasma metanephrines → adrenal imaging → alpha-blockade → adrenalectomy → then thyroidectomy. Skipping straight to thyroid surgery is the wrong-answer trap.

Pharmacotherapy — First-Line Drug Regimens

— Alpha-blockade first: phenoxybenzamine (irreversible, nonselective) 10 mg BID titrated up, or doxazosin (selective α1, fewer side effects, increasingly first-line). Goal BP <130/80 sitting with mild orthostasis.

— High-sodium diet (>5 g/day) and liberal fluids to expand intravascular volume after alpha-blockade.

— Beta-blockade added only AFTER adequate alpha-blockade (usually day 3–5) to control reflex tachycardia — propranolol or atenolol. Never give beta-blocker first — unopposed alpha stimulation causes hypertensive crisis.

— Calcium-channel blockers (nicardipine) as adjunct or alternative.

— Definitive treatment is surgical. Cinacalcet (calcimimetic) for non-surgical candidates or persistent disease — lowers calcium and PTH.

— Bisphosphonates/denosumab for hypercalcemic crisis or bone protection.

— High-dose PPI is mainstay — omeprazole 60 mg daily or higher, titrated to control symptoms and heal ulcers. Continue indefinitely even after attempted resection.

Pheochromocytoma preoperative blockade (10–14 days before surgery):

Hyperparathyroidism:

Gastrinoma (ZES):

Insulinoma: diazoxide (suppresses insulin release) and dietary management bridge to surgical resection.

Prolactinoma: cabergoline (preferred over bromocriptine — better tolerated, weekly dosing) first-line even for macroadenomas; surgery only if drug-resistant or apoplexy.

Acromegaly: surgery first; somatostatin analogs (octreotide LAR, lanreotide), pegvisomant, or cabergoline if residual disease.

MTC advanced/metastatic: vandetanib or cabozantinib (multi-kinase RET inhibitors); newer selpercatinib and pralsetinib (selective RET inhibitors) for RET-altered MTC — superior efficacy and tolerability, preferred when available.

Board pearl: The "alpha-before-beta" rule is the single most tested pharmacology fact in MEN — administering a beta-blocker to an unblocked pheochromocytoma patient causes catastrophic unopposed alpha vasoconstriction.

Procedures and Invasive Management

— MEN2B: <1 year of age, often within first 6 months; central neck dissection if calcitonin >40 pg/mL or imaging-detected disease.

— MEN2A codon 634: by age 5.

— Lifelong levothyroxine replacement; calcium/PTH monitoring postoperatively for transient or permanent hypoparathyroidism.

— Laparoscopic cortical-sparing adrenalectomy preferred when feasible, particularly in MEN2 with bilateral disease, to preserve glucocorticoid function and avoid lifelong steroid replacement.

— Intraoperative anesthesia: ensure adequate alpha-blockade, hydration, arterial line, large-bore IV access. Expect hypotension after tumor removal — fluids and pressors ready.

— MEN1: subtotal (3.5-gland) parathyroidectomy with transcervical thymectomy (removes ectopic parathyroid tissue and reduces thymic carcinoid risk) OR total parathyroidectomy with forearm autotransplantation. Higher recurrence than sporadic PHPT (~50% by 10 years).

— MEN2A: usually single or double adenoma; targeted resection sufficient. Performed at same time as thyroidectomy when possible.

— Insulinoma: enucleation or distal pancreatectomy.

— Gastrinoma: controversial in MEN1 — duodenotomy with duodenal exploration, regional lymphadenectomy. Many advocate observation with PPI for small tumors due to indolent course.

— Nonfunctional NET >2 cm: distal pancreatectomy or Whipple based on location.

Prophylactic total thyroidectomy is the cornerstone of MEN2 management:

Adrenalectomy for pheochromocytoma:

Parathyroidectomy:

Pancreatic NET resection:

Pituitary surgery: transsphenoidal resection for non-prolactin macroadenomas, drug-resistant prolactinomas, or apoplexy.

CCS pearl: In the CCS pheochromocytoma case, your sequence is: confirm with metanephrines → start phenoxybenzamine → add beta-blocker after 3–5 days → high-salt diet → schedule laparoscopic adrenalectomy at 10–14 days → intraoperative monitoring → postop stress-dose steroids if bilateral adrenalectomy.

Special Populations — Elderly and Renal/Hepatic Impairment

— Many MEN1 patients now live into their 70s due to surveillance; new diagnoses in elderly are uncommon but possible (later-onset prolactinomas, NETs).

— Frailty and competing comorbidities shift decisions toward less aggressive surgery — small asymptomatic pancreatic NETs may be surveilled rather than resected.

— Bone health critical: post-menopausal women with prior PHPT and parathyroidectomy still need DEXA every 2 years and vitamin D repletion.

— Hypercalcemia of PHPT accelerates CKD via nephrocalcinosis and nephrolithiasis; aggressive surgical correction in MEN1 prevents progression.

— Cinacalcet is renally cleared but does not require dose adjustment; monitor calcium closely — risk of hypocalcemia.

— Phenoxybenzamine and doxazosin: no specific renal dose adjustment, but start low in CKD due to orthostasis risk.

— Gadolinium MRI: avoid in eGFR <30 (NSF risk) — use non-contrast MRI or DOTATATE PET as alternatives for pituitary/pancreas surveillance.

— Contrast CT requires hydration protocols in CKD; consider MRI when feasible.

— Many NETs metastasize to liver; hepatic metastases drive both prognosis and drug choice.

— Cabergoline is hepatically metabolized — caution in liver disease, monitor LFTs.

— Multi-kinase inhibitors (vandetanib, cabozantinib) require LFT monitoring and dose reduction in moderate hepatic impairment.

— Selpercatinib/pralsetinib: monitor LFTs; dose adjust for elevated transaminases.

— Diazoxide for insulinoma: caution in cirrhosis due to fluid retention.

Older adult MEN patients:

Renal impairment considerations:

Hepatic impairment:

Post-adrenalectomy elderly: bilateral adrenalectomy patients require lifelong hydrocortisone + fludrocortisone; elderly are particularly vulnerable to Addisonian crisis during illness — emphasize stress-dose teaching and medical alert ID.

Step 3 management: In an elderly MEN1 patient on cinacalcet with new CKD stage 4, continue cinacalcet but monitor calcium weekly during dose titration; do not stop abruptly — rebound hypercalcemia can precipitate AKI.

Special Populations — Pregnancy and Pediatrics

— Pheochromocytoma in pregnancy carries maternal mortality up to 50% if undiagnosed — screen MEN2 women preconception or at first prenatal visit.

— If pheo diagnosed in pregnancy: alpha-blockade with phenoxybenzamine (crosses placenta but is the standard); adrenalectomy in 2nd trimester preferred; if diagnosed in 3rd trimester, manage medically and perform cesarean + adrenalectomy.

— Hypercalcemia in pregnancy increases miscarriage, preterm labor, and neonatal hypocalcemic tetany — parathyroidectomy in 2nd trimester is safe and often indicated.

— Prolactinomas: cabergoline generally stopped at confirmed pregnancy for microadenomas; macroadenomas may require continuation with monitoring of visual fields.

— Offer preimplantation genetic diagnosis (PGD) to known MEN1/MEN2 mutation carriers — autosomal dominant transmission with 50% offspring risk.

— Optimize disease control (calcium, BP, prolactin) before conception.

— MEN2B infants: RET testing at birth if known family mutation; prophylactic total thyroidectomy in first 6–12 months of life, before MTC develops.

— MEN2A codon 634: thyroidectomy by age 5; central neck dissection added if calcitonin elevated.

— Annual calcitonin from age 3 in MEN2A; metanephrines from age 11; calcium from age 11.

— Surveillance begins age 5 (prolactin, IGF-1, pituitary MRI every 3 years), expanding through adolescence.

— Children rarely require surgery before adulthood unless symptomatic insulinoma, large pancreatic NET, or symptomatic PHPT.

Pregnancy in MEN syndromes:

Preconception counseling:

Pediatric MEN2 management (the most heavily tested pediatric MEN topic):

Pediatric MEN1:

Genetic testing of minors: ethically appropriate for MEN2 because intervention (thyroidectomy) prevents disease; testing before age 5 is standard for RET. For MEN1, testing typically deferred until age 5 when surveillance starts.

Board pearl: The single most important pediatric MEN intervention is prophylactic thyroidectomy in RET-positive children — it converts a near-certain cancer death into a manageable hypothyroidism.

Complications and Adverse Outcomes

— Metastasis to cervical nodes, lung, liver, bone — drives mortality in MEN2.

— Paraneoplastic Cushing syndrome (ectopic ACTH from MTC) — refractory hypokalemia and hyperglycemia.

— Diarrhea from calcitonin or prostaglandin excess in advanced disease.

— Hypertensive crisis with stroke, MI, aortic dissection, cardiomyopathy (catecholamine-induced reversible LV dysfunction).

— Intraoperative hemodynamic collapse if inadequately blocked.

— Post-adrenalectomy adrenal insufficiency (bilateral cases).

— Nephrolithiasis, nephrocalcinosis, CKD progression.

— Osteoporosis, fragility fractures, osteitis fibrosa cystica (rare).

— Hypercalcemic crisis: AKI, altered mentation, arrhythmia.

— Post-parathyroidectomy hungry bone syndrome: rapid skeletal remineralization → profound hypocalcemia, hypomagnesemia, hypophosphatemia — requires IV calcium and aggressive replacement.

— Gastrinoma: perforated/bleeding peptic ulcers, malabsorption, esophageal stricture.

— Insulinoma: neuroglycopenic injury, seizures, hypoglycemia unawareness, weight gain.

— VIPoma: severe dehydration, hypokalemia → arrhythmia.

— Liver metastases → carcinoid-like syndrome from foregut tumors.

— Recurrent laryngeal nerve injury (hoarseness, airway compromise if bilateral) and permanent hypoparathyroidism after thyroidectomy.

— Lifelong glucocorticoid dependence after bilateral adrenalectomy → risk of adrenal crisis during illness.

MTC-related complications:

Pheochromocytoma complications:

Hyperparathyroidism complications:

Pancreatic NET complications:

Pituitary complications: visual field defects, hypopituitarism, pituitary apoplexy (sudden headache, ophthalmoplegia, hypotension — endocrine emergency requiring stress-dose steroids).

Surgical complications:

Step 3 management: Postoperative day 1 after parathyroidectomy in MEN1 — monitor serial calcium every 6 hours; perioral numbness, Chvostek/Trousseau signs, or QT prolongation triggers IV calcium gluconate plus oral calcitriol and calcium carbonate. Magnesium replacement is essential because hypomagnesemia perpetuates hypocalcemia.

When to Escalate Care — ICU, Consult, and Inpatient Triage

— Pheochromocytoma crisis: severe hypertension with end-organ damage, catecholamine cardiomyopathy with pulmonary edema or cardiogenic shock — admit to ICU with arterial line, IV phentolamine or nicardipine, careful fluid management.

— Pituitary apoplexy: emergent neurosurgical consultation, stress-dose hydrocortisone (100 mg IV then 50 mg q6h), urgent MRI, possible transsphenoidal decompression.

— Hypercalcemic crisis (Ca >14 mg/dL with AKI or altered mentation): aggressive IV NS, calcitonin, IV bisphosphonate (zoledronic acid), consider hemodialysis if refractory.

— Postop thyroidectomy hematoma with airway compromise: bedside wound opening to evacuate, emergent reintubation.

— Adrenal crisis post-bilateral adrenalectomy: IV hydrocortisone 100 mg, fluids, dextrose.

— Endocrinology: longitudinal management and surveillance.

— Endocrine surgery: high-volume center referral improves outcomes (>50 thyroidectomies/year cutoff).

— Medical genetics/genetic counseling: cascade testing, reproductive options.

— Medical oncology: advanced/metastatic MTC or pancreatic NET requiring systemic therapy.

— Interventional radiology: hepatic embolization for symptomatic NET liver metastases.

— Neurosurgery: pituitary disease.

— Outpatient workup for stable hypercalcemia, asymptomatic nodules, surveillance imaging.

— Admit for: hypercalcemia >14, symptomatic pheochromocytoma with poorly controlled BP, refractory ulcer bleeding from gastrinoma, symptomatic hypoglycemia from insulinoma, new pituitary apoplexy.

ICU-level care indications:

Multidisciplinary consults required:

Inpatient vs outpatient triage:

Referral to specialized MEN center improves outcomes — preoperative tumor board for any planned MEN surgery.

CCS pearl: A patient with known MEN2 presenting with chest pain, BP 230/130, and pulmonary edema → don't reflexively give beta-blocker. Order plasma metanephrines, start IV phentolamine or nicardipine, ICU admission, cardiology and endocrinology consults. Beta-blockade only after alpha-blockade is established.

Key Differentials — Same-Category (Endocrine) Causes

— Sporadic: single adenoma (~85%), older age, no family history. MEN1: 4-gland hyperplasia, younger onset, recurrence common.

— Familial hypocalciuric hypercalcemia (FHH): autosomal dominant CASR mutation, asymptomatic mild hypercalcemia, 24-h urine calcium-to-creatinine clearance ratio <0.01 — do not operate (mistaken parathyroidectomy is a classic error).

— Sporadic: usually unilateral, single. MEN2: often bilateral, multifocal, younger onset.

— Other hereditary pheo syndromes: von Hippel-Lindau (VHL; pheo + renal cell carcinoma + hemangioblastomas + pancreatic cysts), neurofibromatosis type 1 (NF1; café-au-lait, neurofibromas), paraganglioma syndromes (SDHB/C/D; head-and-neck and abdominal paragangliomas, SDHB highly malignant).

— All MTC patients require germline RET testing — 25% of "sporadic" MTC are actually hereditary.

— Familial MTC (FMTC) is now considered a variant of MEN2A with MTC-only phenotype.

— MEN4 (CDKN1B mutation): rare; phenocopy of MEN1 with parathyroid, pituitary, and other tumors but no germline MEN1 mutation.

— Carney complex: PRKAR1A mutation; cardiac myxomas, lentigines, primary pigmented nodular adrenocortical disease, acromegaly, Sertoli cell tumors.

— McCune-Albright (mosaic GNAS): polyostotic fibrous dysplasia, café-au-lait, precocious puberty, GH excess — not heritable.

— Hyperparathyroidism-jaw tumor syndrome (CDC73/HRPT2): parathyroid carcinoma + ossifying fibromas of jaw.

Sporadic primary hyperparathyroidism vs MEN1/MEN2A PHPT:

Sporadic pheochromocytoma vs MEN2:

Sporadic MTC vs hereditary MTC:

Other multi-tumor endocrine syndromes:

Polyglandular autoimmune syndromes (APS-1, APS-2): multiple endocrine failures, not tumors — Addison + hypoparathyroidism + mucocutaneous candidiasis (APS-1) or Addison + autoimmune thyroid + type 1 DM (APS-2).

Key distinction: Hypocalciuria with hypercalcemia = FHH, not PHPT — surgery has no role and would not correct calcium. Always check 24-h urine calcium before parathyroidectomy.

Key Differentials — Other-Category Causes

— Marfan: FBN1 mutation, ectopia lentis, aortic root dilation/dissection, mitral valve prolapse, no MTC or pheo, no mucosal neuromas.

— MEN2B: no lens or aortic disease, mucosal neuromas + MTC.

— Common causes: H. pylori, NSAIDs.

— Red flags for ZES/gastrinoma: ulcers in atypical locations (jejunum), multiple ulcers, refractory to standard PPI, diarrhea, hypercalcemia (consider MEN1).

— Reactive, postprandial, drug-induced (especially sulfonylureas — measure sulfonylurea screen), alcohol, adrenal insufficiency, factitious (insulin injection: high insulin, low C-peptide).

— Insulinoma: hypoglycemia with high insulin AND high C-peptide AND high proinsulin plus negative sulfonylurea screen.

— Classic carcinoid (midgut, serotonin-secreting): flushing, diarrhea, right-sided valvular heart disease.

— MEN1 foregut carcinoids (thymic, bronchial): often nonsecretory, present as mass lesions; thymic carcinoid is a leading cause of MEN1 death.

Marfan syndrome vs MEN2B (both marfanoid):

Neurofibromatosis type 1: café-au-lait macules, axillary freckling, Lisch nodules, neurofibromas — can have pheochromocytoma but not MTC.

Tuberous sclerosis: facial angiofibromas overlap with MEN1, but TSC adds shagreen patches, ash-leaf spots, cortical tubers, cardiac rhabdomyomas, renal angiomyolipomas.

Recurrent peptic ulcer disease:

Hypoglycemia in non-diabetic adult:

Secondary causes of hypertension: renovascular (fibromuscular dysplasia, atherosclerotic RAS), primary aldosteronism, Cushing, obstructive sleep apnea, coarctation — distinguish from pheo by aldosterone/renin ratio, dexamethasone suppression, imaging.

Pituitary incidentaloma vs MEN1 pituitary tumor: ~10% of population has pituitary incidentaloma on MRI; MEN1 tumors tend to be larger, more aggressive, more often plurihormonal.

Carcinoid syndrome vs MEN1 foregut carcinoid:

Board pearl: Marfanoid habitus + lens dislocation = Marfan (FBN1); marfanoid habitus + bumpy lips/tongue + thyroid mass = MEN2B (RET). The eye exam is the fastest discriminator.

Secondary Prevention, Discharge Medications, and Long-Term Plan

— Levothyroxine at full replacement dose (~1.6 mcg/kg/day); TSH suppression to low-normal in MTC patients (less aggressive than differentiated thyroid cancer — MTC is not TSH-dependent).

— Calcium carbonate 1–2 g elemental + calcitriol 0.25–0.5 mcg BID for transient hypocalcemia; taper based on calcium and PTH at 2-week and 6-week visits.

— Patient education: signs of hypocalcemia (perioral numbness, cramps, Chvostek/Trousseau).

— Hydrocortisone 15–25 mg/day divided (or prednisone 5 mg daily) + fludrocortisone 0.1 mg daily if bilateral.

— Stress-dose education: double dose for febrile illness; IM emergency hydrocortisone 100 mg kit; medical alert bracelet.

— Vitamin D repletion (cholecalciferol), oral calcium as needed.

— Annual calcium, PTH, 25-OH vitamin D, creatinine, 24-h urine calcium.

— DEXA every 1–2 years.

— Annual calcium/PTH, prolactin, IGF-1, fasting gastrin (off PPI when feasible), chromogranin A, glucose/insulin.

— Pituitary MRI every 3 years; abdominal MRI/EUS every 1–3 years; thymus/lung CT every 1–2 years (especially male smokers).

— Annual calcitonin and CEA post-thyroidectomy; rising values warrant imaging for recurrence.

— Annual plasma/urine metanephrines for life.

— Annual calcium/PTH for MEN2A.

Post-thyroidectomy discharge regimen:

Post-adrenalectomy (especially bilateral or cortical-sparing with insufficiency):

Post-parathyroidectomy:

MEN1 lifelong surveillance (start ages noted in chunk 6):

MEN2 lifelong surveillance:

Gastrinoma: lifelong high-dose PPI; vitamin B12 monitoring (PPI causes B12 malabsorption).

Family screening cascade: ensure all first-degree relatives undergo genetic counseling and testing — frequently missed and a common Step 3 vignette pivot.

Step 3 management: Every MEN patient discharge note must include: (1) confirmed surveillance schedule, (2) endocrinology follow-up within 4–6 weeks, (3) genetic counseling referral for family, (4) medical alert ID if bilateral adrenalectomy.

Follow-Up, Monitoring Parameters, and Counseling

— Endocrinology: every 6–12 months lifelong; more frequent (every 3–6 months) in first year after surgery or with active disease.

— Endocrine surgery: postop visits at 2 weeks, 6 weeks, 6 months, then annually for surveillance imaging review.

— Genetics: at diagnosis, before reproductive decisions, and when new family members are identified.

— Primary care: integrate routine preventive care; ensure surveillance labs are not missed in transitions between specialists.

— Calcitonin doubling time post-thyroidectomy: <6 months predicts aggressive disease; 6–24 months intermediate; >24 months indolent.

— CEA doubling time correlates with prognosis similarly.

— Metanephrines: any elevation triggers cross-sectional imaging.

— Calcium trends: a rising calcium with PTH in mid-normal range may signal MEN1 recurrence years after subtotal parathyroidectomy.

— Reproductive options: PGD, prenatal testing (CVS or amniocentesis), donor gametes, adoption.

— Disclosure to family: encourage proband to inform first-degree relatives; clinicians cannot bypass patient consent except in rare ethically defined circumstances.

— Lifestyle: hydration and moderate dietary calcium for stone prevention; smoking cessation (thymic carcinoid risk in MEN1); avoid sympathomimetics (decongestants, stimulants) until pheo excluded.

— Mental health: chronic surveillance burden, cancer anxiety, survivor guilt — screen for depression and offer psychology referral.

— Post-thyroidectomy voice therapy if recurrent laryngeal nerve dysfunction.

— Bone-health rehab after parathyroidectomy with osteoporosis: weight-bearing exercise, fall prevention.

Visit cadence after diagnosis:

Specific monitoring parameters:

Counseling content:

Rehabilitation considerations:

Transitions of care: pediatric-to-adult endocrinology handoff at age 18–21 is high-risk for missed surveillance — formal transition program recommended.

Board pearl: Calcitonin doubling time <6 months is the strongest single prognostic marker in MTC — drives decisions about systemic therapy (selpercatinib/pralsetinib) and intensifies imaging surveillance.

Ethical, Legal, and Patient Safety Considerations

— Testing children for MEN2 is ethically justified because prophylactic thyroidectomy in infancy/childhood prevents lethal MTC — the standard is to test as soon as possible after birth in known RET families.

— Testing for MEN1 is typically deferred to age 5 (when surveillance benefits begin); testing earlier provides no clinical benefit and removes the child's future autonomy to choose.

— Parental consent and assent of older children required; document discussion.

— Physicians have an ethical duty to encourage probands to share genetic information with first-degree relatives.

— The clinician generally cannot disclose to relatives without patient consent (HIPAA, confidentiality), except in rare jurisdictional carve-outs.

— Document offer of family-letter assistance and genetic counseling referrals.

— Parents consenting to thyroidectomy in an asymptomatic infant must understand lifelong levothyroxine, risks of hypoparathyroidism and recurrent laryngeal nerve injury, and the alternative (near-certain MTC if untreated). Formal multidisciplinary counseling is the standard.

— GINA (Genetic Information Nondiscrimination Act) protects against health insurance and employment discrimination based on genetic test results but does not cover life, disability, or long-term care insurance — disclose this gap during pre-test counseling.

— A common Step 3 vignette: a 20-year-old MEN2 patient leaves pediatric care, misses surveillance, and presents with metastatic MTC. Prevent by structured handoff with documented care plan.

— Bilateral-adrenalectomy patients need a medical alert ID, written stress-dose plan, and emergency IM hydrocortisone kit — failure to provide is a safety event.

Genetic testing of minors:

Duty to inform at-risk relatives:

Informed consent for prophylactic surgery:

Insurance and genetic discrimination:

Transition-of-care safety:

Mandatory reporting: not specific to MEN, but suspected child neglect (untreated RET-positive child whose parents decline thyroidectomy) raises difficult ethics — engage hospital ethics committee rather than unilateral action.

Step 3 management: When a 35-year-old patient newly diagnosed with MEN2A refuses to inform his siblings, the correct action is continued counseling and offering anonymized family letters, not breach of confidentiality.

High-Yield Associations and Rapid-Fire Clinical Facts

MEN1 = 3 Ps: Parathyroid (95%), Pancreas (40–70%), Pituitary (30–40%). Gene: MEN1 on 11q13 (menin, tumor suppressor).

MEN2A = 2 Ps + MTC: MTC, Pheochromocytoma, Parathyroid. Gene: RET on 10q11.2 (proto-oncogene, gain-of-function).

MEN2B = MTC + Pheo + Mucosal neuromas + Marfanoid. No hyperparathyroidism. RET M918T in >95%.

Most common functional pancreatic NET in MEN1 = gastrinoma; most common overall NET = nonfunctional.

Most common pituitary tumor in MEN1 = prolactinoma.

First manifestation of MEN1 = hyperparathyroidism (90%+).

First manifestation of MEN2 = MTC, often detected by screening calcitonin or genetic testing.

Most common cause of death: MEN1 → pancreatic NET or thymic carcinoid; MEN2 → MTC.

Most common cause of perioperative death in MEN2 → unrecognized pheochromocytoma.

Alpha-before-beta in pheo preop blockade.

Calcitonin = MTC tumor marker; chromogranin A = pancreatic NET marker; metanephrines = pheo marker.

DOTATATE PET/CT = modern functional imaging for NETs.

Thymic carcinoid in MEN1 → male smokers; bronchial carcinoid → female MEN1 patients.

FHH mimics PHPT but urine Ca/Cr clearance ratio <0.01 — do NOT operate.

Hungry bone syndrome after parathyroidectomy in long-standing severe PHPT — profound hypocalcemia.

Cinacalcet: calcimimetic for PHPT non-surgical candidates.

Cabergoline first-line for prolactinoma, even macroadenomas.

Selpercatinib/pralsetinib: selective RET inhibitors for advanced RET-mutant MTC.

Cortical-sparing adrenalectomy preferred in MEN2 bilateral pheo to preserve cortisol function.

MEN1 hyperparathyroidism surgery = subtotal 3.5-gland or total + autotransplant, with transcervical thymectomy.

GINA protects health and employment but NOT life/disability/long-term care insurance.

Key distinction: Marfan = lens + aorta; MEN2B = lips + thyroid. Both look marfanoid, but the associated organs make the diagnosis.

Board Question Stem Patterns

Stem 1 — The recurrent ulcer + kidney stone: A 32-year-old man with recurrent duodenal ulcers despite PPI, mild hypercalcemia (Ca 11.2), and a brother with a pituitary tumor. Next step? → MEN1 evaluation: serum calcium, PTH, fasting gastrin, prolactin, IGF-1; genetic testing; family screening.

Stem 2 — The young hypertensive with a thyroid nodule: A 28-year-old woman with episodic palpitations, BP 180/110, and a 1.5 cm thyroid nodule. Next step? → Plasma free metanephrines BEFORE thyroid biopsy or surgery; rule out pheochromocytoma first.

Stem 3 — The bumpy-lipped teenager: A tall, thin 15-year-old with everted lips, tongue nodules, constipation, and a thyroid mass. Diagnosis? → MEN2B; next step is calcitonin, RET testing (expect M918T), metanephrines, then thyroidectomy with central neck dissection.

Stem 4 — Wrong-drug-first pheo: A patient with pheochromocytoma is started on metoprolol and develops severe hypertension and pulmonary edema. Explanation? → Unopposed alpha stimulation; should have received alpha-blockade first (phenoxybenzamine).

Stem 5 — The new infant in a known MEN2A family: A 6-month-old whose father has MEN2A (codon 634). Next step? → RET gene testing; if positive, prophylactic thyroidectomy by age 5.

Stem 6 — The hypercalcemia that isn't PHPT: Young adult, family history of mild hypercalcemia, asymptomatic, Ca 11.1, PTH mid-normal, urine Ca low. Next step? → 24-hour urine calcium-to-creatinine clearance ratio; <0.01 = FHH, do NOT operate.

Stem 7 — Postop hypocalcemia: Day 2 post-parathyroidectomy in MEN1, perioral numbness and Chvostek sign. Diagnosis? → Hungry bone syndrome; IV calcium gluconate, oral calcium carbonate + calcitriol, replete magnesium.

Stem 8 — The MEN1 patient who refuses to tell siblings: Best response? → Continued counseling, offer family letter and genetic counselor support — do not breach confidentiality.

Stem 9 — Pituitary apoplexy: Sudden headache, ophthalmoplegia, hypotension in known MEN1. Next step? → IV stress-dose hydrocortisone immediately, urgent MRI, neurosurgery consult.

CCS pearl: When a vignette gives you "MTC + episodic hypertension," your single highest-yield order is plasma free metanephrines — every downstream decision flows from that result.

One-Line Recap

MEN1 (menin, 11q13) = parathyroid + pancreas + pituitary; MEN2A (RET) = MTC + pheo + parathyroid; MEN2B (RET M918T) = MTC + pheo + mucosal neuromas + marfanoid — and in every MEN2 patient, pheochromocytoma must be excluded before any other surgery.

Genetic-first management: Identify the proband, confirm with MEN1 or RET testing, then perform cascade testing of all first-degree relatives — this single action saves more lives than any drug.

Sequencing rule: In MEN2, always rule out pheo first, treat pheo before MTC, and use alpha-blockade before beta-blockade. Prophylactic thyroidectomy timing is determined by RET codon-specific ATA risk category (HST → infancy, H → by age 5, MOD → by school age).

Surveillance is the long game: Annual biochemistry (calcium/PTH, calcitonin/CEA, metanephrines, prolactin, IGF-1, gastrin, chromogranin A) plus periodic imaging (DOTATATE PET/CT, pituitary MRI, neck US, adrenal CT/MRI) detect tumors when curable.

Common Step 3 traps: giving beta-blocker before alpha in pheo; operating on FHH; missing family screening; failing to start stress-dose steroids after bilateral adrenalectomy; ignoring transition-of-care surveillance gaps in young adults.

Board pearl: If you remember only one MEN fact for Step 3: a thyroid nodule plus episodic hypertension means metanephrines before scalpel — and RET testing is mandatory in every MTC patient, even apparently sporadic.