Clinical presentation Type 1 MEN * Hyperparathyroidism is most common initial clinical manifestation of type s multiple endocrine neoplasia (MEN). * Some patients may manifest findings of ZES before they have hyperparathyroidism. * Symptoms of gastrinoma may become clinically apparent either with abdominal pain and diarrhea or with complications such as ulcer perforation or bleeding. Type 2A MEN * All patients develop MTC on the basis of C-cell hyperplasia. * About 5o% of patients with MTC manifest pheochromocytomas (usually late in life), and 2o% of patients have hyperparathyroidism. Type 2B MEN * Pheochromocytomas occur earlier than in patients with type 2A MEN. Ref : Harrison's Principles of Internal Medicine 21st ed