MKSAP Quiz: Pruritic rash on elbows and knees
A 27-year-old man is evaluated for a pruritic rash on his elbows and knees of 3 years' duration. Celiac disease was diagnosed 7 months ago. He started a gluten-free diet, and the diarrhea resolved but the rash has persisted. He is otherwise well and describes no additional symptoms. He is taking no medications.
On physical examination, vital signs are normal. Skin findings are shown.
Laboratory testing reveals a tissue transglutaminase IgA level of 2 U/mL (normal, 0-3 U/mL).
Skin biopsy findings are consistent with dermatitis herpetiformis.
Which of the following is the most appropriate management?
A. Dapsone
B. Hydrocortisone cream
C. Hydroxychloroquine
D. Measurement of glucose-6-phosphate dehydrogenase activity
Answer and critique
The correct answer is D. Measurement of glucose-6-phosphate dehydrogenase activity. This content is available to MKSAP 19 subscribers as Question 92 in the Gastroenterology and Hepatology section.
The most appropriate management is measurement of glucose-6-phosphate dehydrogenase activity (Option D). This patient with a history of celiac disease has a chronic pruritic vesicular rash on the elbows and knees. Dermatitis herpetiformis is a neutrophilic dermatosis caused by IgA antibodies against tissue and epidermal transglutaminase. It typically presents with intensely pruritic papules and fragile vesicles that rapidly break, leaving tiny erosions. A skin biopsy specimen will show numerous neutrophils stuffing the dermal papillae, and a granular pattern of IgA deposition will be seen on direct immunofluorescence. Most patients with dermatitis herpetiformis will have an underlying gluten-sensitive enteropathy. However, they are usually free of gastrointestinal symptoms; only 20% of patients with celiac disease will develop dermatitis herpetiformis. The distribution and morphology, in the context of a history of celiac disease, are compatible with dermatitis herpetiformis. This condition is treated with a gluten-free diet, but patients may have continued symptoms despite strict adherence to this diet. Such patients may respond to dapsone (Option A). Before initiation of dapsone therapy, it is necessary to check for glucose-6-phosphate dehydrogenase deficiency because individuals with this condition can develop hemolytic anemia when exposed to this medication. Methemoglobinemia, agranulocytosis, and a dapsone hypersensitivity reaction are additional adverse effects. If the patient exhibits normal glucose-6-phosphate dehydrogenase activity, dapsone can be initiated.
Topical glucocorticoids, such as hydrocortisone (Option B), can be helpful as an adjuvant treatment for pruritus in patients with dermatitis herpetiformis, but they are ineffective as monotherapy in inducing remission. When topical glucocorticoids are used, they should be administered along with dapsone and a gluten-free diet. Systemic glucocorticoids, such as prednisone, are usually ineffective in the treatment of dermatitis herpetiformis.
Hydroxychloroquine (Option C) is an immunomodulator that is widely used in systemic lupus erythematosus (SLE) and can be used as monotherapy to treat mild skin and joint symptoms. A rare variant of acute cutaneous lupus presents with vesicles and bullae; invariably, however, these patients have other systemic manifestations of SLE. Therefore, treatment with hydroxychloroquine is not indicated in this patient.
Key Points
- Dermatitis herpetiformis typically presents with intensely pruritic papules and fragile vesicles that rapidly break, leaving tiny erosions, and is commonly associated with histologic and serologic evidence of celiac disease.
- Dermatitis herpetiformis responds rapidly to dapsone; testing for glucose-6-phosphate dehydrogenase deficiency is required before initiation of therapy.
