Dermatitis herpetiformis

What is dermatitis herpetiformis?

Dermatitis herpetiformis (DH) is a skin condition causing a very itchy rash. It is due to intolerance to gluten, which is a natural substance (a protein) found in certain foods. Gluten is in wheat, rye and barley. Gluten intolerance also causes a gut condition called doença celíaca, which is closely linked to DH.

The cause of dermatitis herpetiformis is gluten intolerance. In this condition, your body reacts to gluten in food. Gluten intolerance is also sometimes called gluten sensitivity.

People with gluten intolerance have a kind of allergy to gluten, but it is not the same as a typical food allergy. With gluten intolerance, the gluten somehow triggers your body's immune system to react against the body's own organs.

This is instead of doing what the immune system normally does, which is to be a defence against infections, etc. This may lead to various symptoms in different parts of your body. With dermatitis herpetiformis, it is your skin which is affected.

It is not known exactly what causes the gluten intolerance in the first place.

Does dermatitis herpetiformis always mean you have coeliac disease?

Gluten intolerance also usually causes inflammation in the gut (in the small intestine). When this happens it is called doença celíaca. Most people with dermatitis herpetiformis have some degree of coeliac disease. However, they may not have had any noticeable symptoms and their coeliac disease may not have been diagnosed. See the separate leaflet called Coeliac Disease for more details.

The rest of this leaflet deals with dermatitis herpetiformis.

• Around 1 in 10,000 people have dermatitis herpetiformis. About 1 in 8 people with coeliac disease will have DH.

• Dermatitis herpetiformis is more common in men than in women and usually starts between ages 30-50 years, although it can occur at any age.

There is an extremely itchy rash. It can affect any part of your skin, but is usually on your elbows, knees, buttocks and scalp. The rash is usually on both sides of your body at the same time (symmetrical). The rash has blisters and/or raised spots (papules) - but the blisters usually get scratched off to leave scabs. There may be burning or stinging on the area before the blisters start.

The rash can vary from week to week but does not usually clear up without treatment.

Dermatitis herpetiformis rash

© Madhero88, CC BY-SA 3.0, via Wikimedia Commons

By Madhero88, CC BY-SA 3.0, via Wikimedia Commons

You may also have symptoms of coeliac disease, such as tummy (abdominal) symptoms or unexplained tiredness. However, some people with coeliac disease have little in the way of symptoms, and dermatitis herpetiformis may be the first sign of coeliac disease.

There are various skin conditions that cause itchy rashes with blisters, so a test is needed to diagnose dermatitis herpetiformis for certain. The test is a a skin biopsy. This involves taking a small sample of skin under local anaesthetic. The sample is examined under the microscope in a laboratory, using a special test to look for antibodies called IgA. This test can reliably diagnose DH.

If dermatitis herpetiformis is suspected, you will usually be offered tests for coeliac disease as well. Exames de sangue can help to show if coeliac disease is likely. If the blood tests are positive, you may be offered a test on the gut (a biopsy to sample the lining of your bowel), which can confirm if you have coeliac disease.

There are two treatments for dermatitis herpetiformis:

• Diet.

• Medicação.

Dieta

In the long term, a diet free of gluten will gradually reduce the dermatitis herpetiformis symptoms and may cure DH completely. (This diet also treats coeliac disease.) However, it can take months or years for the diet to improve DH. Therefore, medication is often needed to bring the skin symptoms under control. See the separate leaflet called Coeliac Disease Diet Sheet for more information about the gluten-free diet. In the UK more information is also available from Coeliac UK - see under 'Further Reading and References', below.

Medicação

Medication helps control the rash quickly. The usual medication for dermatitis herpetiformis is dapsone. Dapsone often stops the itching within two days. Dapsone may have side-effects, including anemia. Therefore, regular check-ups and blood tests are needed while you are taking it.

Dapsone is used to treat certain skin conditions, including DH. Exactly how it works is not known. However, it seems to have anti-inflammatory and antibacterial actions. In dermatitis herpetiformis, it is probably the anti-inflammatory action that is helpful.

If you cannot take dapsone or you have side-effects from it, other alternative medicines are available - for example, sulfasalazine or sulfapyridine.

Dermatitis herpetiformis itself does not usually cause complications. However, the gluten intolerance and coeliac disease, if untreated, may make you ill and have possible complications. Most of these problems can be prevented or treated by following a gluten-free diet, which treats both dermatitis herpetiformis and coeliac disease.

Untreated, dermatitis herpetiformis tends to go up and down in severity, but usually continues.

With treatment, the outlook (prognosis) is very good, as dermatitis herpetiformis clears up with medication and a gluten-free diet. Dapsone usually improves the rash quickly. The gluten-free diet takes longer to help - it may take a year or more to get the full benefit. About 8 in 10 people with dermatitis herpetiformis have good results from the diet so they can either stop taking dapsone, or can reduce the dose.