A 38-year-old man of Indian descent presents with a 2-year history of recurrent nephrolithiasis and persistent hypercalcemia (serum calcium 11.2 mg/dL, corrected). On further questioning, he reports a family history of early-onset peptic ulcer disease in his father and thyroid nodules in his sister. Physical examination reveals a palpable thyroid nodule and mild facial asymmetry. Serum PTH is elevated at 85 pg/mL (normal 15–65). Fasting gastrin level is 450 pg/mL (normal <100). Upper endoscopy shows multiple peptic ulcers in the duodenum. Which of the following is the most likely diagnosis?

Explanation

## Diagnosis: MEN 1 Syndrome ### Clinical Presentation Analysis This patient presents with the classic triad of MEN 1: 1. **Primary hyperparathyroidism** — hypercalcemia, elevated PTH, recurrent nephrolithiasis 2. **Gastrinoma (Zollinger-Ellison syndrome)** — elevated fasting gastrin (450 pg/mL), recurrent peptic ulcers 3. **Pituitary or thyroid involvement** — thyroid nodule, family history of thyroid disease ### Key Pathophysiology **Key Point:** MEN 1 is caused by inactivating mutations in the MEN1 gene (chromosome 11q13), which encodes menin, a tumor suppressor protein. Loss of menin function leads to uncontrolled proliferation of neuroendocrine cells in the parathyroids, pancreatic islets, and anterior pituitary. ### MEN 1 Diagnostic Criteria **High-Yield:** The "3 P's" of MEN 1: - **P**arathyroids (95% of patients) — primary hyperparathyroidism, usually multiglandular - **P**ancreas (60–70%) — gastrinomas (most common functional tumor), insulinomas, non-functional tumors - **P**ituitary (20–65%) — prolactinomas most common, followed by growth hormone-secreting and non-functional adenomas ### Differential Features | Feature | MEN 1 | MEN 2A | MEN 2B | | --- | --- | --- | --- | | **Gene** | MEN1 (11q13) | RET (10q11) | RET (10q11) | | **Parathyroid** | Yes (95%) | Yes (20–50%) | No | | **Medullary thyroid cancer** | No | Yes (100%) | Yes (100%) | | **Pheochromocytoma** | No | Yes (50%) | Yes (50%) | | **Gastrinoma** | Yes (60%) | No | No | | **Mucosal neuromas** | No | No | Yes | | **Marfanoid habitus** | No | No | Yes | **Clinical Pearl:** Gastrinomas in MEN 1 are often multiple, located in the gastrinoma triangle (junction of cystic and common bile ducts, junction of pancreatic neck and body), and have a higher malignancy risk than sporadic gastrinomas. ### Screening Recommendations for MEN 1 1. **Biochemical screening** — serum calcium, PTH, fasting gastrin, prolactin, IGF-1 2. **Imaging** — abdominal ultrasound or CT/MRI for pancreatic tumors; pituitary MRI 3. **Genetic testing** — MEN1 gene sequencing in all suspected cases and family members 4. **Age of onset** — hyperparathyroidism typically appears by age 20–25; gastrinomas by age 30–40 **Mnemonic:** **"MEN 1 = 3 P's + Gastrin"** — Parathyroids, Pancreas (gastrin), Pituitary, plus the gastrinoma signature. ### Management - **Parathyroid surgery** — subtotal parathyroidectomy or total parathyroidectomy with autotransplantation - **Gastrinoma** — proton pump inhibitors (PPI) for acid suppression; surgical resection if localized and resectable - **Pituitary adenoma** — dopamine agonists for prolactinomas; surgery if large or causing mass effect - **Genetic counseling** — family screening and surveillance starting in childhood