Endocrinology · Endocrine Neoplasia Syndromes
The facts most likely to be tested
MEN1 is caused by an autosomal dominant germline mutation in the MEN1 tumor suppressor gene located on chromosome 11q13.
The classic clinical triad of MEN1 consists of primary hyperparathyroidism, pancreatic neuroendocrine tumors (pNETs), and pituitary adenomas.
Primary hyperparathyroidism is the most common and earliest manifestation, typically presenting with hypercalcemia and nephrolithiasis.
Gastrinoma (Zollinger-Ellison syndrome) is the most common functional pNET in MEN1, leading to refractory peptic ulcer disease and chronic diarrhea.
Prolactinoma is the most common pituitary adenoma associated with MEN1, often presenting with galactorrhea, amenorrhea, or bitemporal hemianopsia.
Diagnosis of MEN1 is confirmed by the presence of two or more classic endocrine tumors or a positive genetic test for the MEN1 mutation.
Screening for MEN1 in asymptomatic mutation carriers involves annual serum calcium, parathyroid hormone (PTH), fasting gastrin, and prolactin levels.
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A 34-year-old woman presents to the clinic with a 3-month history of recurrent epigastric pain that is poorly responsive to standard proton pump inhibitor therapy. She also reports polyuria and polydipsia. Laboratory studies reveal hypercalcemia, elevated serum gastrin, and elevated prolactin levels. Her family history is significant for a father who underwent surgery for a parathyroidectomy and a pituitary tumor.
What is the most likely underlying genetic diagnosis?
Multiple Endocrine Neoplasia Type 1 (MEN1)
The patient presents with the classic '3 Ps' of MEN1 (parathyroid, pancreas, and pituitary involvement), which is confirmed by the presence of hypercalcemia, gastrinoma, and prolactinoma.
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High yield triage
Etiology / Epidemiology
Autosomal dominant mutation of the MEN1 tumor suppressor gene (menin protein) on chromosome 11q13.
Clinical Manifestations
The 3 Ps: Primary hyperparathyroidism, Pancreatic tumors (gastrinoma/insulinoma), and Pituitary adenomas.
Diagnosis
Clinical diagnosis via genetic testing or presence of 2 of 3 classic tumors; serum calcium and PTH are initial screens.
Treatment
Surgical resection of symptomatic tumors; avoid prophylactic surgery unless indicated by specific guidelines.
Prognosis
Life expectancy is reduced by malignant transformation of pancreatic neuroendocrine tumors; requires lifelong surveillance.
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Epidemiology & Etiology
MEN1 is an autosomal dominant disorder characterized by the loss of function of the menin tumor suppressor protein. It typically presents in the 3rd or 4th decade of life. Nearly 100% of patients develop clinical manifestations by age 50.
Pertinent Anatomy
The syndrome involves the parathyroid glands, the endocrine pancreas (islets of Langerhans), and the anterior pituitary gland. Involvement of the duodenum and bronchial/thymic carcinoids may also occur.
Pathophysiology
The MEN1 gene mutation leads to a loss of cell cycle regulation, resulting in multi-glandular hyperplasia or neoplasia. Parathyroid hyperplasia is typically the earliest manifestation, occurring in >90% of patients. Pancreatic tumors often secrete Zollinger-Ellison syndrome (gastrinoma) or insulin.
Clinical Manifestations
Patients present with primary hyperparathyroidism (hypercalcemia, nephrolithiasis). Pancreatic involvement manifests as Zollinger-Ellison syndrome (refractory peptic ulcers) or insulinoma (hypoglycemia). Pituitary adenomas (often prolactinomas) cause visual field defects or galactorrhea.
Diagnosis
Diagnosis is confirmed by genetic testing for the MEN1 mutation. Biochemical screening includes serum calcium, PTH, fasting gastrin, and prolactin levels. Imaging with CT or MRI is used to localize tumors once biochemical abnormalities are identified.
Treatment
Management is tumor-specific: parathyroidectomy for hyperparathyroidism, proton pump inhibitors for gastrinomas, and dopamine agonists (e.g., cabergoline) for prolactinomas. Avoid total parathyroidectomy to prevent permanent hypoparathyroidism; subtotal resection is preferred. Surgical debulking is indicated for malignant pancreatic neuroendocrine tumors.
Prognosis
Prognosis is primarily determined by the behavior of pancreatic neuroendocrine tumors, which are the leading cause of disease-related mortality. Patients require annual biochemical screening and periodic imaging to detect recurrence or new tumor development.
Differential Diagnosis
MEN2A: Medullary thyroid cancer, pheochromocytoma, and parathyroid hyperplasia
MEN2B: Medullary thyroid cancer, pheochromocytoma, and mucosal neuromas
Zollinger-Ellison Syndrome: Sporadic gastrinoma without parathyroid or pituitary involvement
Prolactinoma: Isolated pituitary adenoma without systemic endocrine involvement
Primary Hyperparathyroidism: Sporadic adenoma without multi-glandular involvement