What is dermatitis herpetiformis?

What is Dermatitis Herpetiformis

Dermatitis herpetiformis (DH) is the cutaneous manifestation of celiac disease, characterized by an intensely itchy, blistering rash typically appearing on the elbows, knees, buttocks, and scalp. 1

Disease Definition and Pathophysiology

DH is an autoimmune blistering disorder that develops in patients with gluten-sensitive enteropathy (celiac disease), presenting as a severely pruritic papulovesicular eruption over extensor surfaces. 2, 3 The condition represents a late manifestation of subclinical celiac disease, where both conditions share the same genetic background (particularly HLA-DQ2/DQ8), gluten-dependent enteropathy, and autoimmune response. 4, 2

The autoimmune response in DH is directed against epidermal transglutaminase (TG3) in the skin, while tissue transglutaminase (TG2) is the autoantigen in the gut. 5, 3 Both TG2-specific autoantibodies appear in serum and small bowel mucosa, but patients with DH additionally have IgA-TG3 antibodies deposited in the skin. 5

Clinical Presentation

The rash manifests as:

• Intensely itchy urticated papules and small blisters 1
• Predilection sites: elbows, knees, buttocks, lower back, neck, and scalp 2, 6
• Symmetrical distribution on extensor surfaces 3

Diagnostic Confirmation

The pathognomonic finding for DH is granular IgA deposits in the papillary dermis demonstrated by direct immunofluorescence of perilesional skin. 2, 3 This finding is used to confirm the diagnosis and distinguishes DH from other blistering disorders. 3

Circulating tissue transglutaminase antibodies (TG2-IgA) support the diagnosis, but their absence does not exclude DH. 2 Small bowel mucosal biopsies are not necessary when DH is diagnosed, though if performed, the majority of patients show villous atrophy, and even those with normal villous architecture demonstrate celiac disease-type inflammation. 2

Epidemiology and Demographics

• DH is slightly more common in males than females, contrasting with celiac disease which shows female predominance 2, 5
• Typically diagnosed during adulthood 2
• Approximately 13% of patients with celiac disease develop DH 7
• The incidence of DH is currently decreasing, in contrast to the four-fold increase in celiac disease incidence 2, 5

Relationship to Celiac Disease

DH is considered one manifestation of celiac disease, with important distinctions:

• One-fourth of DH patients do not have small bowel mucosal villous atrophy, but virtually all have celiac-type inflammatory changes 5
• Gastrointestinal symptoms and the degree of villous atrophy are less obvious in DH than in celiac disease 5
• Five percent of first-degree relatives may be affected by either condition 5
• The skin symptoms in DH are noted as an extra-intestinal manifestation of celiac disease 4

Common Pitfalls

• Do not rely on negative TG2-IgA serology to exclude DH, as circulating antibodies may be absent despite active disease 2
• The skin rash responds slowly to gluten-free diet (taking months to years), which differs from the more rapid intestinal response seen in celiac disease 2, 6
• Clinical features alone cannot reliably distinguish DH from other forms of dermatitis without immunofluorescence confirmation 3