Glucagonoma

Glucagonoma is a rare pancreatic alpha-cell tumor that secretes excess glucagon, and USMLE Step 1 tests it through its classic Five Ds presentation. Students consistently confuse it with insulinoma — both are pancreatic islet cell tumors, but they do opposite things to blood sugar. Glucagonoma causes mild hyperglycemia (essentially mild diabetes), not hypoglycemia. The exam either gives you the rash description (necrolytic migratory erythema) and asks you to name the tumor, or gives you the full syndrome and asks what's driving the hyperglycemia.

The tricky part is that students mix up glucagonoma with insulinoma. Both are pancreatic islet cell tumors, but they do opposite things to blood sugar. Glucagonoma causes mild hyperglycemia (essentially mild diabetes), not hypoglycemia — and students who haven't thought this through carefully get it backwards. The other classic miss is failing to recognize necrolytic migratory erythema: a blistering, crusting, migratory rash of the perineum and extremities that is pathognomonic for glucagonoma. If you see that rash description anywhere on USMLE Step 1, glucagonoma should be the first thing in your head.

Management is simple and testable: somatostatin analogs (octreotide) to suppress glucagon secretion, plus surgical resection if feasible. Glucagonoma is often metastatic at diagnosis, so knowing octreotide as the medical control option matters. Master the Five Ds — Dermatitis (NME), Diabetes, DVT, Depression, Diarrhea — and you've covered almost everything Step 1 will ask.