1.2.7 Dermatitis Herpetiformis

The prevalence is 10.4 per 100,000 individuals and the annual incidence is 1.3 per 100,000 persons. Epidemiology may vary greatly in different countries. M>F, 20-70 years.

Granular depositis of IgA antibodies directed against epidermal transglutaminase precipitate in the dermal papillae and lead to sub-epidermal blister formation. The IgA autoantibodies are most likely triggered by the enteropathy. Neutrophilic infiltration in the dermal papillae. On small bowel biopsy, more that 90% of patients have a gluten-sensitive enteropathy. The intestinal involvement may be like a minimal infiltration of the lamina propria by lymphocytes, to a minimal atrophy of the jejunum associated to an intraepithelial lymphocytic infiltrate, to a complete atrophy of the villi in the small intestine.

A strong association exist between dermatitis herpetiformis and Hashimoto thyroiditis; also, an augmented incidence of enteropathy-associated T-cell lymphoma, but it is rare. It is important to perform investigations for the possibly complications related to malabsorption such as iron deficiency anemia, B12/folate levels, bone densitometry for osteoporosis, and a dental examination; ataxia, central and peripheral nervous system defects and myopathies may be potential neurologic sequelae.

Histology and DIF, with the demonstration of IgA deposition in papillary dermis. IgA anti- transglutaminase antibodies in serum. Small bowel biopsy is optional and not mandatory for the diagnosis. Gluten-sensitive enteropathy confirmed in over 90% of patients but symptomatic in only 15%. Rapid symptom relief with dapsone.

Other autoimmune bullous dermatoses (bullous pemphigoid, pemphigus vulgaris), especially linear IgA disease (no gluten-sensitive enteropathy), eczema, arthropod bites, scabies, urticarial vasculitis.

Gluten-free diet, characterized by a wheat, rye and barley diet exclusion, and dapsone. Dapsone is important to relieve the itch and the lesions, but it has no effects on enteropathy. Prior to starting dapsone, it is recommended to measure glucose-6-phosphate dehydrogenase. The initial dose of dapsone is 25- 50 mg/daily, and then usually a dose of 100 mg/daily if needed. Whilst on dapsone monitor for side effects, such as agranulocytosis, anemia, methaemoglobinemia, hepatitis and peripheral neuropathy. Another drug used is sulfasalazine.