A 31-year-old man comes to the physician because of worsening abdominal pain, an inability to concentrate at work, and a general lack of motivation over the past several months. He has a history of spontaneous passage of two kidney stones. His father and uncle underwent thyroidectomy before the age of 35 for thyroid cancer. Physical examination shows diffuse tenderness over the abdomen. Serum studies show: Na+ 142 mEq/L K+ 3.7 mEq/L Glucose 131 mg/dL Ca2+ 12.3 mg/dL Albumin 4.1 g/dL Parathyroid hormone 850 pg/mL Further evaluation is most likely to show elevated levels of which of the following?

Serum aldosterone to renin ratio

Urine 5-hydroxyindoleacetic acid

A 47-year-old woman complains of weight gain and irregular menses for the past 2 years. She has gained 13 kg (28.6 lb) and feels that most of the weight gain is in her abdomen and face. She has type 2 diabetes and hypertension for 1 year, and they are difficult to control with medications. Vital signs include a temperature of 36.9°C (98.4°F), blood pressure of 160/100 mm Hg, and pulse of 95/min. The patient's late-night salivary cortisol is elevated. Morning plasma ACTH is high. Brain magnetic resonance imaging shows a 2 cm pituitary adenoma. Which of the following is the optimal therapy for this patient?

Transsphenoidal pituitary adenomectomy

A 21-year-old male college student is very anxious about having thyroid cancer as he found a lump in his neck a few days ago. He has also had diarrhea and a feeling of warmth on his face for 3 days now. His father and uncle both have been diagnosed with thyroid cancer. The lump is about 1 cm in diameter and is fixed and nontender on palpation. Physical examination is otherwise unremarkable. Ultrasound shows a non-cystic cold nodule that requires fine needle aspiration for diagnosis. Thyroid functions tests are normal, and his calcitonin level is 346 ug/ml. Which of the following genetic mutations would warrant thyroidectomy in this patient?

Down expression of the Ras protooncogene

Activating mutation of the BRAF gene

A 67-year-old woman with tertiary hyperparathyroidism and end-stage renal disease on hemodialysis has persistent hypercalcemia (calcium 12.8 mg/dL) despite maximal medical management with cinacalcet and vitamin D restriction. She has severe pruritus, calciphylaxis, and vascular calcifications. All four parathyroid glands are enlarged on imaging. Evaluate the optimal surgical strategy considering her complex medical status and need for ongoing dialysis access.

Total parathyroidectomy with forearm autotransplantation

Single adenoma resection guided by sestamibi

Subtotal parathyroidectomy (3.5 gland resection)

Total parathyroidectomy without autotransplantation

Medical management escalation with denosumab

A 30-year-old man presents with a 6 cm adrenal mass discovered incidentally. Biochemical workup shows elevated 24-hour urine metanephrines and plasma free metanephrines. He also has elevated serum calcium, PTH, and a pancreatic head mass on CT. Genetic testing confirms MEN 2B syndrome. Evaluate the management priorities and sequencing of interventions.

Adrenalectomy first, then thyroidectomy, then other tumors

Simultaneous thyroidectomy and bilateral adrenalectomy

Medical management of pheochromocytoma then parathyroidectomy

Immediate thyroidectomy followed by staged procedures

Pancreatic surgery first due to mass effect

A 38-year-old woman with primary hyperparathyroidism (calcium 11.8 mg/dL, PTH 185 pg/mL) has negative sestamibi scan and ultrasound. She desires surgical cure and has no medical contraindications. She has a Z-score of -2.8 on DEXA scan and a history of recurrent kidney stones. Evaluate the surgical approach and expected outcomes.

Bilateral neck exploration with identification of all four glands

Defer surgery until localization studies are positive

Minimally invasive parathyroidectomy of the largest gland

Medical management with cinacalcet and bisphosphonates

Intraoperative PTH-guided focused exploration

Multiple endocrine neoplasia syndromes — USMLE Lesson

🧬 Genetic Dominoes

Inherited as Autosomal Dominant traits with high penetrance. A single mutated allele is sufficient to predispose to cancer.
Caused by germline mutations in specific genes:
- MEN1 gene (Chr 11): A tumor suppressor gene. Requires a loss-of-function mutation.
- RET proto-oncogene (Chr 10): A receptor tyrosine kinase. Requires a gain-of-function mutation.

⭐ Knudson's "Two-Hit" Hypothesis (for MEN1): Individuals inherit one mutated allele (1st hit). A later somatic mutation inactivates the second, normal allele (2nd hit), leading to tumor development.

Knudson Two-Hit Hypothesis in MEN1 Syndrome

🧬 Pathophysiology - The MENagerie

Multiple Endocrine Neoplasia (MEN) syndromes are inherited autosomal dominant disorders causing synchronous or metachronous tumors in multiple endocrine glands.

MEN1 gene (Chr 11): Encodes menin, a tumor suppressor. Follows Knudson's "two-hit" hypothesis for loss of function.
RET gene (Chr 10): A proto-oncogene (receptor tyrosine kinase). A single "one-hit" gain-of-function mutation is sufficient for tumorigenesis.

📌 Mnemonic:

MEN 1 = 3 P's
MEN 2A = 2 P's, 1 M
MEN 2B = 1 P, 2 M's

Syndrome	Gene	Key Tumors & Presentation
MEN 1	MEN1	Parathyroid adenomas (most common, hypercalcemia), Pituitary adenomas (prolactinoma), Pancreatic neuroendocrine tumors (gastrinoma, insulinoma)
MEN 2A	RET	Pheochromocytoma (often bilateral), Parathyroid hyperplasia (hypercalcemia), Medullary Thyroid Carcinoma (MTC)
MEN 2B	RET	Pheochromocytoma, Medullary Thyroid Carcinoma (MTC, more aggressive), Mucosal neuromas (lips, tongue), Marfanoid habitus

MEN syndromes: Clinical features comparison

🧬 Diagnosis - Catching the Syndromes

Initial Step: Biochemical screening based on clinical presentation.
MEN 1 Screen:
- Serum calcium, PTH, gastrin, prolactin.
MEN 2A/2B Screen:
- Plasma free metanephrines (or urinary fractionated metanephrines).
- Serum calcitonin (basal or stimulated).
- MEN 2A: Also check serum calcium & PTH.
Confirmation: Genetic testing (MEN1 or RET proto-oncogene) is the gold standard for diagnosis and screening at-risk relatives.

⭐ All patients with medullary thyroid cancer (MTC) should undergo RET proto-oncogene testing. If positive, screen for pheochromocytoma before thyroidectomy to prevent hypertensive crisis.

🔪 Management - Surgical & Medical Plays

MEN 1 (Wermer's Syndrome):
- Parathyroid: Subtotal (3.5 glands) or total parathyroidectomy with forearm autotransplantation.
- Pancreatic (pNETs): Surgical resection for insulinomas/gastrinomas. PPIs for gastrinoma symptoms.
- Pituitary: Transsphenoidal surgery. Dopamine agonists (e.g., cabergoline) for prolactinomas.
MEN 2A (Sipple's Syndrome):
- Pheochromocytoma: Resect FIRST. Pre-op α-blockade (phenoxybenzamine) then β-blockade.
- Medullary Thyroid Cancer (MTC): Prophylactic total thyroidectomy by age 5.
- Parathyroid: Resection only if hyperparathyroidism is present.
MEN 2B:
- Pheochromocytoma: Same as MEN 2A (resect first).
- MTC: Prophylactic total thyroidectomy by age 1 (more aggressive).

⭐ 💡 In MEN 2, always resect the pheochromocytoma before thyroidectomy to prevent life-threatening intraoperative hypertensive crisis. "Pheo first!"

⚡ Biggest Takeaways

MEN 1 (Wermer's): 3 P's - Parathyroid adenomas (most common), Pancreatic tumors (e.g., gastrinoma), Pituitary adenoma. Due to MEN1 gene mutation.

MEN 2A (Sipple's): 2 P's, 1 M - Pheochromocytoma, Parathyroid hyperplasia, Medullary thyroid cancer (MTC). RET proto-oncogene mutation.

MEN 2B: 1 P, 2 M's - Pheochromocytoma, Medullary thyroid cancer (MTC), Mucosal neuromas/Marfanoid habitus. RET mutation.

Key Action: Always screen for pheochromocytoma before other surgeries.

Prophylaxis: Prophylactic thyroidectomy is indicated for all patients with RET mutations.

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