Question 138

Question:

A 31-year-old man presents to the emergency room complaining of weakness, palpitations, diaphoresis, and irritability. He has had several similar episodes in the past few weeks, none as severe as this one. Physical exam is unremarkable. The nurse performs a fingerstick to check his blood glucose, which is found to be 39. Administration of glucose relieves his symptoms. Serum calcium is 11.1. A mass in which of the following structures is likely responsible for his presenting symptoms?

Correct Answer: B.  Pancreas

This patient’s presenting symptoms and hypoglycemia raise the possibility of an insulinoma, although there are other possibilities (adrenal insufficiency, hypopituitarism, hepatic insufficiency). An insulinoma is a tumor of the beta cells of the pancreatic islets. Over 99% of insulinomas originate in the pancreas. They are associated with MEN-I syndome (pituitary, pancreas, parathyroid neoplasms), which is important in this case because this patient is hypercalcemic, which may be due to parathyroid hyperplasia. Approximately 90% of patients with MEN-I syndrome have parathyroid hyperplasia.
For this patient, C-peptide and proinsulin levels should be checked prior to further studies to rule out the possibility of insulin self-injection. CT and other localizing tests could then be performed. About 80% of insulinomas are benign, solitary adenomas that are cured with surgical resection.