Coeliac Disease You Can See
Dermatitis herpetiformis (DH) is the cutaneous manifestation of coeliac disease, affecting approximately 10 to 15 percent of coeliac patients. Named for its resemblance to herpes simplex vesicles (though it has no viral connection), DH presents as intensely pruritic, grouped vesicles and papules symmetrically distributed on the elbows, knees, buttocks, back, and scalp. The itch is often the most debilitating symptom — described by patients as burning or stinging — and may precede visible lesions.
The Immunological Mechanism
DH is caused by IgA deposits at the tips of dermal papillae. The target autoantigen is epidermal transglutaminase (eTG, or TG3), a homologue of the tissue transglutaminase (tTG, or TG2) targeted in intestinal coeliac disease. IgA anti-eTG antibodies form immune complexes that deposit in the papillary dermis, activating complement and recruiting neutrophils. The resulting neutrophilic microabscesses at the dermal-epidermal junction cause the characteristic blister formation.
Direct immunofluorescence (DIF) of perilesional skin — not the blister itself — shows granular IgA deposits at the dermal papillae. This finding is pathognomonic for DH and is the diagnostic gold standard. Biopsy of the active lesion itself shows neutrophilic infiltration but may miss the diagnostic IgA pattern.
The Gut Connection
Remarkably, 75 to 90 percent of DH patients have villous atrophy on duodenal biopsy, even though many have minimal or no gastrointestinal symptoms. The remaining 10 to 25 percent show Marsh 1-2 changes (increased IELs or crypt hyperplasia). Essentially, DH patients have coeliac disease that manifests primarily through the skin rather than the gut.
Serological markers follow the same pattern as intestinal coeliac disease: tTG-IgA and EMA are positive in the majority (though titres may be lower than in patients with severe villous atrophy). Anti-eTG antibodies can be measured but are not widely available in routine clinical practice.
Treatment: Two-Track Approach
The long-term treatment is a strict gluten-free diet, which resolves both the skin and intestinal manifestations — though skin improvement takes longer (months to years) than intestinal healing. For immediate symptom relief, dapsone (diaminodiphenyl sulfone) is the drug of choice. Dapsone suppresses neutrophil chemotaxis and inhibits the complement-dependent damage, providing itch relief within 24 to 48 hours. However, dapsone has significant side effects (haemolysis, methaemoglobinaemia, agranulocytosis) and requires monitoring of full blood count, reticulocytes, and methaemoglobin levels.
As the GFD takes effect, dapsone can gradually be tapered. Some patients eventually achieve complete control with diet alone, while others require low-dose maintenance dapsone. The combination of GFD plus dapsone as bridging therapy is the standard of care.
DH as a Protective Factor?
Intriguingly, epidemiological data suggest that DH patients have a lower risk of developing enteropathy-associated T cell lymphoma compared to coeliac patients without DH, possibly because their disease comes to clinical attention earlier through the visible skin manifestation, leading to earlier dietary intervention.