Dermatitis herpetiformis

What is dermatitis herpetiformis and who gets it?

Dermatitis herpetiformis (also known as ‘DH’) is a rare but persistent blistering skin condition related to coeliac disease.

Dermatitis herpetiformis is an ‘immunobullous’ condition, which means it is a blistering condition caused by an abnormal immunological reaction. Like other forms of coeliac disease, it involves IgA antibodies and intolerance to the gliaden fraction of gluten found in wheat, rye and barley.

Dermatitis herpetiformis often affects young adults; two thirds of patients are male. There is a genetic predisposition; there are associations with human leukocyte antigens (HLAs) DQ2 DQ8.

Eighty percent of patients with dermatitis herpetiformis also have gluten enteropathy, the most common form of coeliac disease. Some patients have personal or family history of other autoimmune disorders.

Dermatitis herpetiformis is unrelated to other forms of dermatitis such as atopic eczema.

Clinical features of dermatitis herpetiformis

Dermatitis herpetiformis is characterised by extremely itchy bumps (prurigo papules) and blisters (vesicles), which arise on normal or reddened skin. They tend to be distributed symmetrically and are most often found on the scalp, shoulders, buttocks, elbows and knees.

As the blisters are so itchy, they are often immediately scratched, resulting in erosions and crusting. Older lesions may leave pale or dark marks (hypopigmentation and hyperpigmentation). Flat red patches, thickened plaques and raised wheals may arise, resembling eczema, scabies and other skin conditions.

Dermatitis herpetiformis

Gluten enteropathy

Gluten enteropathy affects the majority of children and adults with dermatitis herpetiformis. It is characterised by small bowel villous atrophy. This means that instead of being highly convoluted, the lining of the intestines is smooth and flattened. The result is poor or very poor absorption of nutrients. The patient may feel well or develop the following symptoms:

• Tiredness (80%)
• Abdominal discomfort and bloating (75%)
• Weight loss (30%)
• Constipation (30%) or diarrhoea (50%)
• Pale stools that float on the surface of the toilet pan
• Bone fractures due to osteoporosis

Other features of coeliac disease

The range of conditions less commonly induced by gluten also includes:

• Neurological problems including ataxia (loss of balance), polyneuropathy, epilepsy
• Heart problems including pericarditis and cardiomyopathy
• Thin dental enamel
• Recurrent abortions (miscarriage)
• Fatty liver resulting in abnormal liver function
• Aphthous ulcers

Patients with coeliac disease sometimes suffer from other autoimmune conditions possibly associated with gluten intolerance. These include insulin-dependent diabetes mellitus, thyroiditis, autoimmune hepatitis, Sjögren's syndrome, Addison's disease, atrophic gastritis and alopecia areata.

They may also be affected by conditions that are not related to gluten intolerance. These include IgA deficiency, psoriasis, Down syndrome and primary biliary cirrhosis.

Non-Hodgkin´s lymphoma, affecting the intestines or any part of the body, is a serious complication of gluten enteropathy but is fortunately rare, affecting less than 1% of patients.

Laboratory findings in dermatitis herpetiformis

Although dermatologists may suspect the diagnosis from the clinical appearance, a skin biopsy is usually necessary to confirm it. The microscopic appearance of dermatitis herpetiformis is characteristic.

• The blister is subepidermal (it forms underneath the epidermis)
• The inflammatory cells (neutrophils and eosinophils) group in the dermal papillae
• Direct immunofluorescence reveals IgA immunoglobulin in dermal papillae

The results of blood tests are usually normal but some patients have the following abnormalities, due to malabsorption associated with gluten enteropathy:

• Mild anaemia
• Folic acid deficiency
• Iron deficiency

Specific autoantibody tests are available to confirm the diagnosis of coeliac disease.

• Antiendomysial antibodies (IgA)
• Tissue transglutamidase antibody, tTG (IgA)
• Deamidated gliadin peptide antibody (dGP, IgA and IgG)
• Gliadin assay (IgA and IgG)

Dermatitis herpetiformisis is associated with IgA antibodies directed against epidermal transgluataminase (eTG).

Borderline results may be difficult to interpret.

Other tests may include:

• Total IgA
• Histocompatibility antigen typing: HLA-DR3 and DQw2 are present in most patients with coeliac disease. About 5% of those with HLA-DQ are affected by one form or other of coeliac disease
• Small bowel biopsy

The bowel may appear normal because of treatment (medicine or restricted intake of gluten), because there are skip lesions (the sample was taken from an unaffected site) or the intestine may be unaffected by the disease.

Treatment

The medication of choice is dapsone, which considerably reduces the itch within a day or two. The dose required varies from 50 mg to 300 mg daily; refer to DermNet's page about dapsone for potential side effects and monitoring requirements.

For those intolerant or allergic to dapsone, the following may be useful:

• Ultrapotent topical steroids
• Systemic steroids
• Sulfapyridine (not available in New Zealand).

A strict gluten-free diet is strongly recommended.

• It reduces the requirement for dapsone
• It improves associated gluten enteropathy
• It enhances nutrition and bone density
• It may reduce the risk of developing other autoimmune conditions
• It probably reduces the risk of intestinal lymphoma.