The patient most likely has celiac sprue (also called gluten-sensitive enteropathy). If untreated, all of the listed diagnoses may be accompanied by findings of chronic diarrhea without clear trigger foods for several years and a chronically wasted appearance with diffuse muscle loss. However, the case patient has a vesicular rash on his extensor surfaces that is intensely pruritic (ie, dermatitis herpetiformis), which is a classic finding in patients with celiac sprue, and is not seen in the context of the other illnesses listed.
