Dermatitis Herpetiformis (DH)

What dermatitis herpetiformis is

Despite its name, DH has nothing to do with the herpes virus. "Herpetiformis" refers to the grouped blisters that look a little like herpes.

In people with a genetic predisposition (HLA-DQ2 or HLA-DQ8 genes), eating gluten, a protein in wheat, barley and rye, triggers an immune response. The body makes IgA antibodies against an enzyme called epidermal transglutaminase. These antibodies settle in the upper skin, causing inflammation, bumps and blisters. The same process in the gut damages the intestinal lining, as in celiac disease.

About 10% or more of people with celiac disease develop DH. Most people with DH have intestinal damage, but fewer than 1 in 5 have obvious digestive symptoms.

Symptoms

• intense itching or burning, often before the rash appears
• clusters of small red bumps and tiny fluid-filled blisters
• symmetrical distribution on the outer elbows, knees, buttocks, lower back, shoulders and scalp
• blisters are often scratched open, leaving crusts and scratch marks rather than intact blisters
• flares and remissions over months to years
• darker or lighter skin left behind as the rash heals

Gut symptoms such as bloating, diarrhea and tiredness may occur, and some people have iron-deficiency anemia.

Conditions it can be confused with

Diagnosis

• Skin biopsy: two samples. One from a blister for routine microscopy, and one from normal-looking skin next to a lesion for direct immunofluorescence. Granular IgA deposits in the dermal papillae confirm DH.
• Celiac blood tests: tissue transglutaminase IgA (tTG-IgA) and total IgA, sometimes endomysial or epidermal transglutaminase antibodies.
• Intestinal biopsy: often not needed if the skin biopsy confirms DH.
• G6PD level: before starting dapsone.
• Other tests: thyroid function and blood count, because autoimmune thyroid disease and anemia are common.

Keep eating gluten until testing is complete, because a gluten-free diet can make blood tests and biopsies falsely negative.

Treatment

Gluten-free diet

A strict, lifelong gluten-free diet is the only treatment that addresses the cause. It heals the gut, eventually clears the rash and lowers the risk of complications. Skin improvement takes time, often 6 months to 2 years, so most people need medicine at first. A dietitian experienced in celiac disease is very helpful.

Dapsone

Dapsone, an antibiotic with anti-inflammatory effects, usually relieves itching within 48 to 72 hours. It does not treat gut damage. Side effects include hemolysis (breakdown of red blood cells), methemoglobinemia (causing blue lips and breathlessness) and, rarely, liver problems, a serious rash or a drop in white blood cells. Regular blood tests are needed. Many people can reduce or stop dapsone after 1 to 2 years on a strict gluten-free diet.

Other options

• Sulfapyridine or sulfasalazine if dapsone is not tolerated
• Potent topical steroids for short-term itch relief
• Antihistamines for itch, though they help less

Complications

• gut complications of celiac disease: malabsorption, anemia and osteoporosis
• other autoimmune conditions: Hashimoto's thyroiditis, type 1 diabetes, pernicious anemia and vitiligo
• a slightly increased risk of intestinal lymphoma, which a strict gluten-free diet reduces

Outlook

DH is a lifelong condition, though some people go into remission. With a strict gluten-free diet, most people become rash-free and can stop medicines. Accidental gluten exposure can cause flares within hours to days.

Frequently asked questions

What does dermatitis herpetiformis look like?

It looks like clusters of small red bumps and tiny blisters, often scratched into crusts, appearing symmetrically on the elbows, knees, buttocks, back and scalp. It is extremely itchy, and itching or burning often comes before the bumps appear.

Is dermatitis herpetiformis the same as celiac disease?

DH is the skin manifestation of celiac disease. Almost everyone with DH has gluten-sensitive changes in the small intestine, even without digestive symptoms. Both are triggered by gluten and treated with a gluten-free diet.

How is dermatitis herpetiformis diagnosed?

It is diagnosed with a skin biopsy taken from normal-looking skin next to the rash, tested with direct immunofluorescence for IgA deposits. Blood tests for celiac antibodies support the diagnosis. You should keep eating gluten until testing is done.

How long does it take for dermatitis herpetiformis to clear on a gluten-free diet?

The rash can take 6 months to 2 years to clear fully on a strict gluten-free diet. Dapsone relieves itching within a few days in the meantime and can often be tapered off as the diet takes effect.

Is dermatitis herpetiformis contagious?

No. Dermatitis herpetiformis is an autoimmune reaction to gluten, not an infection. It cannot be spread to others by contact, and it is not related to the herpes virus.