What Is Dermatitis Herpetiformis?
 
 
   


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The following article, written by Lionel Fry, Emeritus Professor of Dermatology, first appeared in the Summer 2001 Edition of the Crossed Grain, the official magazine of Coeliac UK, and is reproduced here with their kind permission.

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Professor Lionel FryDescribed by one sufferer as

"...like rolling in stinging nettles naked with a severe sunburn, then wrapping yourself in a wool blanket filled with ants and fleas...."

Dermatitis herpetiformis (DH) was first described as a distinct clinical entity in 1884 by an American dermatologist, Louis Duhring. The name was descriptive, dermatitis being inflammation of the skin and herpetiformis meaning group. The typical features are small grouped itchy blisters, often on red plaques, situated on the back of the elbows and forearms, buttocks and front of the knees. Although these are the common sites the rash may in addition, occur anywhere on the body including face, scalp and trunk. The eruption is extremely itchy and may keep patients awake at night.

DH may be present at any age but most commonly begins between the ages of 15-40. It is slightly more common in men than females at a ratio of 3:2. DH is a persistent condition and only approximately 10% of patients have a spontaneous permanent remission. It is a rare disease in the UK with the incidence being approximately 1:15,000.

Role of gluten and association to coeliac disease

The first suggestion that patients with DH also have an enteropathy identical to coeliac disease (CD) was made in 1967. This was confirmed by showing the enteropathy cleared with gluten withdrawal from the diet and recurred when gluten was reintroduced. It was subsequently shown that all patients with DH have evidence of a gluten enteropathy. However, in the majority of patients the enteropathy is mild and does not give rise to symptoms such as abdominal pain, weight loss and diarrhoea. Thus, all patients with DH have associated CD although it could be described as latent CD in the majority.

Diagnosis

The diagnosis of DH is made by a simple skin test. A small piece of skin approximately 3 mms in diameter is taken from an unaffected area, ie. normal looking skin. The skin is examined for the presence of a substance called IgA (immunoglobulin A) and is found at a specific site in the skin. Although the test is simple, it is important a laboratory experienced in the procedure undertakes the examination of the skin.
 
The diagnosis of DH can also be confirmed with the same tests as used for diagnosing CD, ie. a small intestinal biopsy and blood tests looking for specific antibodies, called anti-endomysial and tissue transglutaminase antibodies. Occasionally in DH, the blood tests may be negative because their positivity correlates strongly with the severity of the intestinal lesion.

Management of DH

Until the discovery of the association of DH with CD the treatment of DH was solely with drugs. Now there is a more satisfactory and less hazardous treatment with a gluten free diet; although, it must be appreciated that drugs will control the rash within days but the diet will not. Therefore, both drugs and diet will be required initially.

Drugs

The drugs more commonly used for the treatment of DH are Dapsone, sulphapyridine, and sulphamethoxypyridazine. All are very early antibiotics dating back to the 1930's and 1940's. However, these drugs do not work as antibiotics but the exact mechanism of action of DH is unknown.

Although the drugs will control the rash of DH very quickly, ie. within days, the rash will recur equally quickly when drugs are discontinued. Thus, drug treatment of DH has to be considered indefinite but it is not a cure for the disease. It is important to find the smallest dose required to control the rash and this varies between patients. Thus, the dose may be increased or decreased after initial treatment.

Unfortunately all three drugs used to control the rash in DH may have side effects.

Dapsone has the highest incidence of side effects. 25% patients will experience an adverse reaction. The commonest reaction is so-called haemolytic anaemia. Others are neuropathy (damage to nerves), depression, headache and (rarely) damage to the liver and bone marrow. It is important that patients taking drugs for DH are carefully monitored with frequent blood tests at the beginning of treatment. Since side-effects tend to occur early in treatment, patients may only have to attend hospital every six months once established on drug treatment.

Gluten-free diet

It is important to appreciate that a gluten free diet may have no effect on the rash for approximately six months and sometimes, even longer. It takes this length of time before patients can start to reduce their drug requirements and approximately 2 years before they can discontinue drugs completely. It is also important to realise that these times are only achieved if the diet is absolutely strict. Even small amounts of gluten may result in patients not being able to stop their drugs.

Thus, because the drugs control the rash quickly and the gluten free diet does not, it is normal practice to start both drugs and diet together. After six months, the dose of drugs can be slowly reduced. DH is a persistent disorder (and because these patients also have CD, even if mild), the diet must be considered to be life-long. However, one improvement for patients that has occurred in the last five years is that it has been shown in DH (as in CD) that oats do not cause the rash and thus, these can be taken. Wheat, barley and rye must still be omitted. There is no evidence that gluten in flour or wheat products touching the skin can induce or exacerbate DH or CD.

Associated disorders

Although, DH is not itself a so-called autoimmune disease, there is an increased incidence of the latter in patients with DH. The three most commonly associated with DH are thyroid disease, pernicious anaemia and diabetes. Thus, patients with DH should be screened for these diseases on a yearly basis. There are other less common autoimmune disorders, which are also increased in DH and these have to be borne in mind during follow-up. There is some evidence that a strict gluten-free diet reduces the risk of developing autoimmune diseases.

Lymphoma (a type of malignancy) also has an increased incidence in DH as in CD. The incidence is approximately 2% but it has been shown that the risk of developing this disorder disappears with a strict gluten-free diet.

Genetics

There is evidence that both DH and CD have a genetic basis. It appears that the genes for the two diseases are fundamentally the same because pairs of identical twins have been described in which one twin has DH and the other only CD. In addition, in large families the relatives of a patient with DH have equal numbers of those affected with DH as with CD. At present, the genes for DH and CD have not been found but there are certain genetic markers for the disease that are known, which appear to increase the susceptibility to the diseases.

The risk of patients with DH having children with the disease is relatively low. In a study of over 1,000 patients with DH in Finland, only 10% of the patients had a family history of the disease and only 14% of these had a child with the disease. However, there are now tests for screening for CD, which is the prerequisite for DH and thus, relatives can be screened if so desired.

The future

It can be said that both patients with DH and CD can now be cured with a treatment, a gluten free diet, which does not require drugs, which is a remarkable achievement compared to many other diseases. However, research will continue into how gluten causes both CD and DH and new treatments may emerge which allow patients to eat a normal diet.

We very much appreciate Professor Fry writing this article. As a footnote, he added that people with Coeliac Disease do significantly reduce their risk of contracting DH if they stick to a gluten-free diet.

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Keywords

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