Dermatitis herpetiformis often occurs in young adults but can occur in children and older people. It is rare in blacks and Asians.
Almost all patients with dermatitis herpetiformis have celiac disease histologically, but in most cases the celiac disease is asymptomatic. Dermatitis herpetiformis develops in 15 to 25% of patients with celiac disease. Patients may have a higher incidence of other autoimmune disorders (including thyroid disorders, pernicious anemia, and diabetes) and small-bowel lymphoma. IgA deposits collect in the dermal papillary tips and attract neutrophils; they can be eliminated by a gluten-free diet.
The term herpetiformis refers to the clustered appearance of the lesions (similar to that seen in herpesvirus infection) but does not indicate a causal relationship to herpesvirus.
Onset of dermatitis herpetiformis can be acute or gradual. Vesicles, papules, and urticarial lesions are usually distributed symmetrically on extensor aspects of the elbows and knees and on the sacrum, buttocks, and occiput. Lesions itch and burn. Because itching is intense and skin is fragile, vesicles tend to rupture quickly, often making intact vesicles difficult to detect. Oral lesions may develop but are usually asymptomatic. Iodides and iodine-containing preparations may exacerbate the cutaneous symptoms.
Diagnosis of dermatitis herpetiformis is based on skin biopsy and direct immunofluorescence testing of a lesion and adjacent (perilesional) normal-appearing skin. Direct immunofluorescence showing granular IgA deposition in the dermal papillary tips is invariably present and important for diagnosis.
All patients with dermatitis herpetiformis should be evaluated for celiac disease. Serologic markers such as IgA anti-tissue transglutaminase antibody, IgA anti-epidermal transglutaminase antibody, and IgA anti-endomysial antibody can help confirm the diagnosis and aid in monitoring disease progression.
Dapsone generally results in remarkable improvement. Initial dosages of dapsone are 25 to 50 mg orally once a day in adults and 0.5 mg/kg in children. Usually, this dose dramatically relieves dermatitis herpetiformis symptoms, including itching and burning, within 1 to 3 days. If improvement occurs, the dose is continued. If no improvement occurs, the dose can be increased every week, up to 300 mg/day. Most patients respond well to 50 to 150 mg/day.
Dapsone can cause hemolytic anemia; risk is highest after 1 month of treatment and is increased in patients who have glucose-6-phosphate dehydrogenase (G6PD) deficiency. Patients suspected of having G6PD deficiency should be tested for this deficiency before being treated with dapsone. Methemoglobinemia is common; hepatitis, agranulocytosis, dapsone syndrome (hepatitis and lymphadenopathy), and a motor neuropathy are more serious complications.
Sulfapyridine 500 mg orally 3 times a day (or, alternatively, sulfasalazine) is an alternative for patients who cannot tolerate dapsone. Doses of sulfapyridine up to 2000 mg orally 3 times a day can be used. Sulfapyridine may cause agranulocytosis.
Patients receiving dapsone or sulfapyridine should have a baseline complete blood count (CBC). CBC is then done weekly for 4 weeks, then every 2 to 3 weeks for 8 weeks, and every 12 to 16 weeks thereafter.
Patients are also placed on a strict gluten-free diet. After initial therapy and disease stabilization, most patients can stop drug therapy and be maintained on the gluten-free diet, but this may take months or years. A gluten-free diet also maximizes improvement in the enteropathy and, if strictly followed for 5 to 10 years, decreases risk of small-bowel lymphoma.
Almost all patients who have dermatitis herpetiformis, even if they have no gastrointestinal symptoms, have histologic evidence of celiac disease and are at risk of small-bowel lymphoma.
Because itching is intense and skin is fragile, vesicles may all be broken and thus not evident on examination.
Confirm the diagnosis with skin biopsy, direct immunofluorescence testing of a lesion and adjacent normal-appearing skin, and serologic tests.
Use dapsone or an alternative drug (eg, sulfapyridine) to control skin manifestations initially.
Have patients try to maintain long-term control with only a strict gluten-free diet so that drug therapy can be stopped.