Dermatitis herpetiformis

Definition

Dermatitis herpetiformis (DH) is characterised by a persistent, itchy blistering skin rash which usually occurs on the knees, elbows, buttocks and back, although can affect any area of skin.  DH results from gluten sensitivity and intestinal biopsy nearly always shows the characteristic flattening of intestinal villi.  However, unlike coeliac disease itself, the gastrointestinal symptoms may be mild and are often not apparent at all; less than 10% of people with DH have gastrointestinal symptoms characteristic of coeliac disease (1). 

All patients with DH have some degree of coeliac disease, and are very likely to reflect the entire spectrum of histologic and clinical coeliac disease in adults.

Prevalence

DH is less common than coeliac disease with a UK incidence of about 1 in 10,000.  It is slightly more common in men than women (ratio of 3:2) and most commonly appears between the ages of 15-40 years; it is rare in children.  DH is much less common in black and Asian populations.  As with coeliac disease, there is an inherited tendency to develop the disease, and there are links with auto-immune thyroid disease and Type 1 diabetes (2) with both patients with DH and family members being at increased risk of developing these disorders (3).

The prevalence of HLA-DQ2 and -DQ8 is the same as in coeliac disease, supporting the concept that DH is a manifestation of coeliac disease (4).

Diagnosis

Patients with DH demonstrate intensely pruritic papulovesicles and excoriations on the elbows, knees, buttocks, and scalp.  Cases rarely present without characteristic involvement of one of these areas.  According to a recent report granular IgA must be present in dermal papillary tips in perilesional skin for a definite diagnosis (4). Biopsy needs to be performed on perilesional skin (clinically normal-appearing skin immediately adjacent to an area of inflammation).  False negatives may occur if a biopsy is performed on involved skin. 

All patients with DH have some degree of coeliac disease, and are very likely to reflect the entire spectrum of histologic and clinical coeliac disease in adults.  No consistent serologic or immunologic difference between patients with DH and patients with coeliac disease has ever been identified. 

Clinically, 10-20% of patients with DH present with classic symptoms of malabsorption and another 20% are estimated to have atypical symptoms, but at least 60% of patients have 'silent' coeliac disease. 
The presence of DH is a marker of coeliac disease that is independent of the severity of histologic coeliac disease or the intestinal symptoms.

Management

The condition is managed by a gluten-free diet and drug treatment.  A gluten-free diet, can often take several months before the rash improves and nearly 2 years before it disappears completely.  Both the skin disease and the intestinal disease recur with reinstitution of a diet containing gluten. 

Drugs, such as Dapsone (Diaminodiphenylsulfone), are an important part of the management of DH.   The cutaneuos disease in DH clears rapidly on treatment with Dapsone, and recurs rapidly if Dapsone is discontinued.  Dapsone has no influence on intestinal abnormality.  Side-effects of Dapsone include haemolytic anaemic, neuropathy, depression, and headache.   

Long term consequences

Many of the long-term implications of coeliac disease are also relevant to patients with DH, including lymphoma (5). The clinical associations include thyroid abnormalities, which occur in 15-20% of patients (6). 

References

1 Reunala T.  Dermatitis herpetiformis: coeliac disease of the skin. Annals of Medicine 1998; 30(5): 416-418

2 Reunala T, Collin P. Diseases associated with dermatitis herpetiformis. British Journal of Dermatology. 1997;136(3):315-8.

3 Hervonen K, Viljamaa M, Collin P, Knip M, Reunala T. The occurrence of type 1 diabetes in patients with dermatitis herpetiformis and their first degree relatives. British Journal of Dermatology 2004; 150(1): 136-138

4 Zone JJ.  Skin manifestations of Celiac Disease.  Gastroenterology 2005; 128: S87-S91

5 Hervonen K. Vornanen M. Kautiainen H. Collin P. Reunala T. Lymphoma in patients with dermatitis herpetiformis and their first-degree relatives. British Journal of Dermatology 2005;152(1):82-6, 2005 Jan.

6 Cunningham MJ, Zone JJ. Thyroid abnormalities in dermatitis herpetiformis: prevalence of clinical thyroid disease and thyroid antibodies. Annals of International Medicine 1985;102:194-196