This patient has dermatitis herpetiformis, which is associated with celiac disease. Dermatitis herpetiformis is a chronic, extremely pruritic autoimmune disorder associated with gluten-sensitive enteropathy, or celiac disease. Although not all patients have gastrointestinal symptoms, nearly 100% of patients will have some underlying abnormality associated with celiac disease. Dermatitis herpetiformis classically presents as extremely pruritic vesicles and papules in a symmetric distribution involving the elbows, knees, buttocks, and scalp. At times, excoriations predominate, and intact vesicles may not be visualized. Although dermatitis herpetiformis is an uncommon skin finding, the association with celiac disease is very high, and the diagnosis should be suspected if the characteristic skin findings are present. Patients with dermatitis herpetiformis are also at risk for other autoimmune conditions, including autoimmune thyroid disease, type 1 diabetes mellitus, and pernicious anemia. There is also a potential association of dermatitis herpetiformis with lymphoma. Treatment is gluten avoidance, although improvement of the rash may occur very slowly over months to years. Dapsone can be used to treat dermatitis herpetiformis and is very effective; however, it can allow persistence of celiac disease, which can result in small bowel lymphoma with chronic inflammation. As a result, dapsone should be used in conjunction with gluten-free diets as first line treatment.

Hepatitis C can occur in association with porphyria cutanea tarda, which presents as vesicles in sun-exposed areas such as the dorsal hands, and resultant milia (small white cysts). Associated hypertrichosis also can be seen.

Non-Hodgkin lymphoma is associated with paraneoplastic pemphigus, which presents as painful oral, conjunctival, or esophageal erosions with associated erythema and blistering on the skin. Paraneoplastic pemphigus always has mucosal involvement, which was absent in this patient's presentation.

Inflammatory bowel disease, including ulcerative colitis, can occur in association with epidermolysis bullosa acquisita, which presents as painful bullae and erosions in areas of trauma, often on extensor surfaces; these lesions heal with scarring and milia. This patient's extreme pruritus makes epidermolysis bullosa acquisita unlikely.