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PostPosted: 17 May 2014 18:53 
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Dermatitis herpetiformis (DH) is an autoimmune blistering skin disease associated with coeliac disease (gluten enteropathy). DH may be considered as a cutaneous manifestation of coeliac
Disease

Aetiology

All forms of coeliac disease involve intolerance to the gliadin fraction of gluten found in wheat; there are IgA antibodies. In DH, IgA antibodies are deposited in the skin. Recent research suggests that coeliac patients with DH have a qualitatively different immune reaction in the intestinal mucosa than those that do not. This results in minimal clinical symptoms, allowing for increased gluten ingestion and cutaneous IgA deposition.

Epidemiology

For coeliac disease, UK prevalence is around 1%.
DH is most common in Caucasians of northern European descent with a prevalence of 11.2 and an incidence of 0.98% per 100,000 people.
There is a male:female preponderance of approximately 2:1.
DH usually presents in the fourth decade but has been reported in children as young as 2 and in the elderly as old as 90.

Presentation.

DH 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 1 cm 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.

Investigations

Skin biopsy
This is usually necessary to confirm the diagnosis. The microscopic appearance of DH is characteristic:
The blister is subepidermal.
Inflammatory cells group in the dermal papillae.
Direct immunofluorescence reveals IgA immunoglobulin in dermal papillae.

Blood tests

These may show abnormalities due to gluten enteropathy; for example:
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 patients. IgA-epidermal transglutaminase 3 is likely to be the most specific immunocomplex in DH.
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.Therefore it may be advisable to measure serum IgA levels to identify cases of IgA deficiency; or to test for IgG endomysial antibodies or IgG-tissue transglutaminase levels.
A small proportion of patients with coeliac disease are tissue transglutaminase antibody-negative (0.4% in one series) and some are endomysial antibody-negative.Detection rates may be improved by combining both tests.

Other possible investigations
A novel serological assay using deamidated gliadin-analogous fusion peptides (GAF3X) showed high diagnostic sensitivity in DH patients with coeliac disease.
Histocompatibility antigen typing: HLA-DR-DQ genotyping is expensive but techniques are being developed to make this more cost-effective in the diagnosis of coeliac disease.
Small bowel biopsy (may appear normal if on a gluten-free diet, or due to skip lesions in the bowel).

Dr G Mohan.

Do request -Differential Diagnosis,Management,Complications,Prognosis: if needed.


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