A 64-year-old woman comes to the office due to a progressive rash. The patient initially had painful, itchy red spots on her right leg 2 months ago, which gradually enlarged and began to crust. Similar spots later appeared on her abdomen and chin. She has used several over-the-counter corticosteroid and antibiotic creams with no improvement. The patient has had no palpitations, abdominal pain, or vomiting, but has had occasional watery stools. She was diagnosed with type 2 diabetes mellitus 6 months ago, and lifestyle modification was advised. The patient does not use tobacco, alcohol, or illicit drugs. Temperature is 37 C (98.6 F), blood pressure is 110/70 mm Hg, pulse is 78/min, and respirations are 14/min. Weight is 10 kg (22 lb) lower than 6 months ago; BMI is 21 kg/m². Physical examination shows erythematous plaques with central clearing and eroded borders on the right thigh. There are scattered papules with crusting over the lower abdomen and in the perioral skin. The remainder of the examination shows no abnormalities. Laboratory studies are significant for a hemoglobin level of 10.2 g/dL and glucose level of 176 mg/dL. Which of the following would be most helpful in establishing the diagnosis in this patient?

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11ec25c8_d3ae_1209_bc81_2d2273c432b0_MD0003_00 This patient with diabetes mellitus, weight loss, diarrhea, and a painful, pruritic rash likely has a glucagonoma, a pancreatic neuroendocrine tumor characterized by the unregulated release of glucagon. Manifestations reflect the effects of glucagon, which increases amino acid oxidation and has catabolic actions. Glucagonoma is often diagnosed late in the disease course due to nonspecific early features; necrolytic migratory erythema (NME) is the presenting feature in ~70% of patients. NME, likely due to amino acid deficiency, is characterized by painful/pruritic papules that coalesce to form large, indurated plaques with scaling and central clearing on the face, groin, and extremities. The excess glucagon also causes hyperglycemia/diabetes mellitus, although this is usually mild and rarely requires insulin. Other common features include weight loss (catabolic action of glucagon), diarrhea (secretion of glucagon and other molecules [eg, secretin]), venous thromboembolism, and neuropsychiatric symptoms (eg, depression, psychosis). Laboratory evaluation typically shows normocytic, normochromic anemia, which may be due to anemia of chronic disease or a direct effect of glucagon on erythropoiesis. A markedly elevated serum glucagon level (>500 pg/mL) confirms the diagnosis. Although glucagon is increased in other conditions (eg, hypoglycemia, Cushing syndrome, pancreatitis), the elevations are typically mild to moderate. Abdominal imaging (CT scan or MRI) can localize the tumor and evaluate for metastases. (Choice A) Antimitochondrial antibodies are associated with primary biliary cholangitis, which presents with diffuse pruritis, jaundice, hepatomegaly, and abnormal liver markers (eg, alkaline phosphatase, aminotransferases). Skin manifestations include xanthomas and hyperpigmentation. (Choice C) Porphyria cutanea tarda causes skin fragility and chronic, scarring blisters and bullae in sun-exposed areas. It is commonly associated with hepatitis C; hepatic aminotransferases are often mildly elevated. Blood counts are typically normal. (Choice D) Vitamin A deficiency most commonly presents with impaired night vision. Skin findings (eg, hyperkeratosis) are usually nonspecific. (Choice E) Tissue transglutaminase IgA antibodies are seen in dermatitis herpetiformis, typically associated with celiac disease. Skin manifestations include grouped, intensely pruritic papules and vesicles on the extensor surfaces of the elbows, knees, back, and buttocks. (Choice F) Niacin deficiency is characterized by photosensitive, pigmented dermatitis (primarily in sun-exposed areas); diarrhea; and neuropsychiatric symptoms (eg, dementia, psychosis). Educational objective: Glucagonomas frequently cause necrolytic migratory erythema, characterized by painful/pruritic papules that coalesce to form large plaques on the face, groin, and extremities. Other manifestations include diabetes mellitus, weight loss, diarrhea, and anemia. A serum glucagon level >500 pg/mL confirms the diagnosis, and abdominal imaging can localize the tumor and evaluate for metastases. References: Glucagonoma syndrome: a review and update on treatment. (http://www.ncbi.nlm.nih.gov/pubmed/27422767)

A 64-Year-Old Woman Comes to the Office Due to a Progressive