Step 1 topics → Endocrine → Glucagonoma

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.

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Common misconceptions

Common mistake
Gap: Missing that necrolytic migratory erythema is the hallmark dermatologic manifestation of glucagonoma
Necrolytic migratory erythema — a blistering, crusting rash of the perineum and extremities — is the pathognomonic skin finding of glucagonoma.
Necrolytic migratory erythema is the dermatologic hallmark of glucagonoma, and you need to recognize it from a description alone. The rash is blistering and crusting, migrates, and preferentially affects the perineum and extremities. When you see this rash in a vignette — especially paired with weight loss, mild diabetes, or DVT — glucagonoma is the diagnosis.
Common mistake
Wrong: Glucagonoma causes hypoglycemia because glucagon is being overproduced and will eventually deplete glucose stores.
Right: Glucagonoma causes hyperglycemia (mild diabetes) because excess glucagon stimulates hepatic glycogenolysis and gluconeogenesis.
Glucagon's job is to raise blood sugar: it drives hepatic glycogenolysis and gluconeogenesis. A glucagonoma floods the body with excess glucagon, so blood sugar goes up — producing mild diabetes, not hypoglycemia. Confusing this with insulinoma (which secretes insulin and causes hypoglycemia) is a common error. Remember: glucagon = glucose up, insulin = glucose down. Glucagonoma mimics insulin deficiency, not insulin excess.
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What the exam tests

  1. Know the Five Ds of glucagonoma (Dermatitis/necrolytic migratory erythema, Diabetes, DVT, Depression, Diarrhea) and be able to identify glucagonoma from a clinical vignette describing this constellation.
  2. Recognize necrolytic migratory erythema as the pathognomonic skin finding of glucagonoma — a blistering, crusting rash affecting the perineum and extremities.
  3. Know that glucagonoma is managed with octreotide (to suppress glucagon release) and surgical resection when possible.

Can you avoid these mistakes?

A 55-year-old woman presents with a blistering, crusting rash around her perineum and inner thighs, mild hyperglycemia, and a recent DVT. What is the most likely diagnosis, and what is the name of the rash?
A patient is found to have a glucagonoma. His fasting blood glucose is 210 mg/dL. A classmate says this must be a lab error because tumors that secrete peptide hormones should cause hypoglycemia from receptor downregulation. What is wrong with this reasoning?
A patient with a metastatic glucagonoma is not a surgical candidate. What is the first-line medical treatment to control hormone hypersecretion, and what is the mechanism by which it reduces glucagon release?
A 60-year-old man presents with a blistering migratory rash, mild diabetes, weight loss, and a history of DVT. Walk through the Five Ds of glucagonoma and identify which single finding would most immediately point you to this diagnosis over other causes.

Related topics

Hypothalamic-Pituitary-Adrenal (HPA) Axis Hypothalamic-Pituitary-Thyroid (HPT) Axis Hypothalamic-Pituitary-Gonadal (HPG) Axis Hormone Signaling (Peptide vs Steroid)

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