Dermatitis herpetiformis: symptoms, causes and treatment

NHS inform says people with DH can have red, raised patches often with blisters that burst with scratching, together with severe itching and often stinging. Coeliac UK uses the same description and adds that the rash is most commonly seen on the elbows, knees and buttocks, but any area of the skin can be affected.

The rash usually occurs symmetrically, meaning on both sides of the body, for example on both elbows.

• Red, raised patches, often with small blisters.

• Severe itching and often stinging.

• Usually on the elbows, knees and buttocks, although any area of skin can be affected.

• Usually on both sides of the body at once.

NHS inform describes it as an autoimmune skin condition, meaning the immune system mistakenly acts against the body's own tissue, and says it can be linked to coeliac disease. Coeliac UK explains that DH is often called simply DH.

The NHS lists an itchy rash called dermatitis herpetiformis among the possible general symptoms of coeliac disease. Because of this link, a diagnosis of DH leads to testing for coeliac disease.

UK sources give slightly different figures. Coeliac UK says DH affects fewer people than typical coeliac disease, at around 1 in 3,300 people, and that it is most commonly diagnosed in those aged between 50 and 69 years old. NHS inform says it affects around 1 in 10,000 people, is most commonly diagnosed between the ages of 15 and 40, is more common in men than women and is rare in children.

Both agree that DH can appear at any age. The differences probably reflect different counting methods, so treat the figures as a rough guide that it is uncommon.

NHS inform says DH is caused by the body's immune system reacting to gluten, a protein found in foods containing wheat, barley and rye. This reaction causes the skin rash to develop.

Coeliac UK says most people with DH have the same kind of gut damage seen with coeliac disease even when they have no gut symptoms, which is why the gluten-free diet is essential even if your digestion feels normal.

NHS inform and Coeliac UK both say diagnosis is confirmed by a skin biopsy. A dermatologist takes a small sample of skin from an area without the rash, because a sample from the rash itself does not always give the right result. Coeliac UK explains that the sample is checked for an antibody called immunoglobulin A (IgA).

If the biopsy is positive you should be referred to a gastroenterologist, who will test for coeliac disease with antibody blood tests and a gut biopsy. Coeliac UK says it is important to keep eating gluten until the blood tests and biopsy are done; if you have already stopped, you must reintroduce gluten in more than one meal every day for at least 6 weeks before the tests.

The treatment for DH is a lifelong gluten-free diet, which means removing all sources of gluten from wheat, barley and rye. Some people may also be sensitive to oats. NHS inform says a gluten-free diet should only start once the diagnosis is given and a referral to a dietitian has been made.

Skin symptoms take longer to recover than the gut symptoms of coeliac disease. Coeliac UK says it can take an average of two years for a gluten-free diet to take full effect, and in some cases longer; NHS inform says up to 2 years or more.

Because the diet takes so long to work, you may be given tablets to control the rash at first. The most common is dapsone, a tablet that works within days to control itching and the development of blisters. The rash returns if you stop it before the diet has taken effect. The most common side effect is anaemia, so your doctor may check for this regularly, and less common effects are headache and depression, with nerve damage rare. You are prescribed the lowest effective dose. For people who cannot tolerate dapsone, sulphapyridine and sulphamethoxypyridazine are alternatives.

NHS inform says DH can cause the same conditions and complications as coeliac disease, including osteoporosis, certain kinds of gut cancer and an increased risk of other autoimmune diseases such as type 1 diabetes and thyroid disease. Coeliac UK makes the same points and both say the risk is reduced by following the gluten-free diet.

Coeliac UK also notes that taking dapsone will not make the gut damage of coeliac disease worse, but that drugs only control skin symptoms, so the diet remains an essential part of treatment.

See a GP if you have a persistent, intensely itchy rash with blisters, particularly on the elbows, knees or buttocks, or if you have a known diagnosis and the rash is flaring. Do not stop eating gluten before testing, because this can make tests unreliable.

If you take dapsone, NHS inform says the lowest effective dose is prescribed and that your condition should be monitored once the dose is reduced, and Coeliac UK says your doctor may check regularly for anaemia. For urgent concerns, NHS 111 can advise.

On the NHS, DH is usually suspected by a GP and confirmed by a dermatologist, who performs the skin biopsy, before a gastroenterologist arranges coeliac testing. A dietitian referral should be made when the diagnosis is confirmed. Private dermatology and gastroenterology services follow the same diagnostic steps.

Coeliac UK offers information and support for people living with coeliac disease and DH, including guidance on gluten-free food and care after diagnosis.