Dermatitis herpetiformis (DH) is an autoimmune blistering skin disease associated with coeliac disease (gluten enteropathy).¹ DH may be considered as a cutaneous manifestation of coeliac disease.²

Aetiology¹

All forms of coeliac disease involve intolerance to the gliadin fraction of gluten found in wheat; there are IgA antibodies. The precise mechanism is unknown.

Epidemiology

• For coeliac disease, UK prevalence is around 1%.³
• Estimates of DH incidence vary. It has been suggested that approximately 15-25% of coeliac disease patients may develop DH.^4,5 Another estimate is that DH affects 1 in 10,000 people.⁶
• DH can appear at any age, but most commonly presents between ages 15-40 years. It is uncommon in children.⁶

Presentation¹

Dermatitis herpetiformis is an intensely itchy bullous rash. It characteristically affects extensor surfaces, particularly the scalp, buttocks, elbows and knees. However, lesions can occur on any area of skin.

• The lesions are papules and blisters, up to 1cm in diameter, which are extremely itchy. They arise on normal or reddened skin. Burning, stinging, and intense pruritus can precede the appearance of new lesions.
• The severity can vary from week to week.
• Lesions rarely resolve without specific treatment.

There may also be symptoms of coeliac disease. To see related article on coeliac disease click here.

Investigations¹

Skin biopsy is usually necessary to confirm the diagnosis. The microscopic appearance of dermatitis herpetiformis is characteristic:

• The blister is subepidermal.
• Inflammatory cells group in the dermal papillae.
• Direct immunofluorescence reveals IgA immunoglobulin in dermal papillae.

Blood tests:

• May show abnormalities due to gluten enteropathy, e.g:
  • Mild anaemia
  • Folic acid deficiency
  • Iron deficiency
• Coeliac disease can usually be detected by autoantibody testing:
  • IgA anti-tissue transglutaminase or IgA endomysial antibodies are highly specific and sensitive for untreated coeliac disease. They are also relevant to DH patients⁷
  • Note that these tests can be falsely negative if the patient:
    • Is already on a gluten-free diet.
    • Has selective IgA deficiency, which is more common in coeliac disease patients than in the general population.⁸ Therefore it may be advisable to measure serum IgA levels to identify cases of IgA deficiency;⁹ or to test for IgG endomysial antibodies.¹⁰
    • A small proportion of patients with coeliac disease are tissue transglutaminase antibody negative (0.4% in one series)¹¹ and some are endomysial antibody negative. Detection rates may be improved by combining both tests.¹²

Other possible investigations:

• Histocompatibility antigen typing: HLA-DR3 and DQw2 are present in most patients with coeliac disease.
• Small bowel biopsy (may appear normal if on a gluten-free diet, or due to skip lesions in the bowel).

Differential diagnosis⁴

• Erythema multiforme
• Herpes gestationis
• Linear IgA bullous dermatosis¹³
• Eczema
• Neurotic excoriations
• Papular urticaria
• Scabies
• Transient acantholytic dermatosis

Management

A strict gluten-free diet is important in order to:¹

• Reduce the medication needed to control skin symptoms. It may be possible to discontinue dapsone when on a gluten-free diet for sufficient time.¹⁴
• Reduce the associated enteropathy, improve nutrition and bone density.
• Possibly, to reduce the risk of developing other autoimmune conditions and intestinal lymphoma.

Drug treatment:^1,4

• Dapsone is first choice, and reduces the itch within a day or two. Cautions and blood monitoring requirements should be noted.
• For those intolerant or allergic to dapsone, the following may be used:
  • Sulfapyridine
  • Ultrapotent topical steroids
  • Systemic steroids
• Avoid drugs which exacerbate DH. These may include NSAIDs (though ibuprofen seems safe) and iodides.

Complications and associated conditions^1,12

Virtually all DH patients have coeliac disease, although it may be unnoticed.¹⁴ Many have thyroid disease (about 30%).

Complications may arise from problems associated with coeliac disease. These include:

• Neurological problems - ataxia (gluten ataxia), peripheral neuropathy, epilepsy.¹²
• Cardiac problems - pericarditis and cardiomyopathy.
• Osteoporosis and poor dental enamel.
• Reduced fertility and recurrent miscarriage.
• Abnormal liver function tests.
• Aphthous ulcers.
• Possibly, other autoimmune conditions: thyroid disease, insulin-dependent diabetes mellitus, autoimmune hepatitis, Sjögren's syndrome, Addison's disease, atrophic gastritis and alopecia areata.
• Non-Hodgkin's lymphoma - affects < 1% of DH patients.¹
• There may be a slightly increased risk of other cancers.¹⁵

Some of these problems may be improved by a gluten-free diet.

Prognosis¹⁴

• Untreated, DH follows a prolonged course over years, with relapses and remissions. It may eventually resolve spontaneously.
• The prognosis is good, as DH responds well to diet and medication:
  • About 80% of patients with dermatitis herpetiformis have good results from a gluten-free diet
  • It may take a year or more of this diet before medication for DH can be reduced⁶
  • Some patients are able to stop dapsone completely with diet treatment