Dermatitis herpetiformis is often misdiagnosed, being confused with drug eruptions, contact dermatitis, dishydrotic eczema (dyshidrosis), and even scabies.
Diagnosis is confirmed by a simple blood test for IgA antibodies, and by a skin biopsy in which the pattern of IgA deposits in the dermal papillae, revealed by direct immunofluorescence, distinguishes it from linear IgA bullous dermatosis and other forms of dermatitis. These tests should be done before the patient starts on a gluten-free diet, otherwise they might produce false negatives. If the patient has already started a gluten-free diet (there is a strong relationship with DH and coeliac sprue), it might be necessary for them to come off it for some weeks before the tests can be done reliably.
Dermatitis herpetiformis responds well to medication and changes in diet.
Dapsone is an effective treatment for most patients. DH responds to dapsone so quickly (itching is significantly reduced within 2–3 days) that this response may almost be considered diagnostic. However, dapsone treatment has no effect on any intestinal damage that might be present.
Therefore, a strict gluten-free diet must also be followed, and this will usually be a lifelong requirement. This will reduce any associated intestinal damage and the risk of other complications. After some time on a gluten-free diet, the dosage of dapsone can usually be reduced or even stopped, although this can take many years.
Dapsone is an antibacterial, and its role in the treatment of DH, which is not caused by bacteria, is poorly understood. It can cause adverse effects on the blood, so regular blood monitoring is required.
Dapsone is the drug of choice, but, for patients unable to tolerate dapsone for any reason, the following can be tried, although they are less effective:
In terms of pathology, the first signs of the condition may be observed within the dermis. The changes that can take place at this level may include edema, vascular dilatation, and cellular infiltration. It is common for lymphocytes and eosinophils to be seen. The bullae found in the skin affected by dermatitis herpetiformis are subepidermal and have rounded lateral borders.
When looked at under the microscope, the skin affected by dermatitis herpetiformis presents a collection of cells known as neutrophils. They have an increased prevalence in the areas where the dermis and is the closest to the epidermis.
Direct IMF studies of uninvolved skin show IgA in the dermal papillae and patchy granular IgA along the basement membrane. The jejunal mucosa may show partial villous atrophy, but the changes tend to be milder than in coeliac disease.
Immunological studies revealed findings that are similar to those of coeliac disease in terms of autoantigens. The main autoantigen of dermatitis herpetiformis is epidermal transglutaminase (eTG), a cytosolic enzyme involved in cell envelope formation during keratinocyte differentiation.
Various research studies have pointed out different potential factors that may play a larger or smaller role in the development of dermatitis herpetiformis. The fact that eTG has been found in precipitates of skin-bound IgA from skin affected by this condition has been used to conclude that dermatitis herpetiformis may be caused by a deposition of both IgA and eTG within the dermis. It is estimated that these deposits may resorb after 10 years of following a gluten-free diet. Moreover, it is suggested that this condition is closely linked to genetics. This theory is based on the arguments that individuals with a family history of gluten sensitivity who still consume foods containing gluten are more likely to develop the condition as a result of the formation of antibodies to gluten. These antibodies cross-react with eTG, and IgA/eTG complexes deposit within the papillary dermis to cause the lesions of dermatitis herpetiformis. These IgA deposits can disappear after long-term (up to 10 years) avoidance of dietary gluten.
DH is an autoimmune disease, and patients with DH are more likely than others to have thyroid problems and intestinal lymphoma.
Dermatitis herpetiformis does not usually cause complications on its own, without being associated with another condition. Complications from this condition, however, arise from the autoimmune character of the disease, as an over-reacting immune system is a sign that something does not work well and might cause problems to other parts of the body that do not necessarily involve the digestive system.
Gluten intolerance and the body’s reaction to it make the disease more worrying in what concerns the possible complications. This means that complications that may arise from dermatitis herpetiformis are the same as those resulting from coeliac disease, which include osteoporosis, certain kinds of gut cancer, and an increased risk of other autoimmune diseases such as thyroid disease.
The risks of developing complications from dermatitis herpetiformis decrease significantly if the patients follow a gluten-free diet. The disease has been associated with auto-immune thyroid disease, insulin-dependent diabetes, lupus erythematosus, Sjögren’s syndrome, sarcoidosis, and vitiligo or alopecia areata.
It has been suggested that French revolutionary Jean-Paul Marat suffered from DH, leading him to spend much of his time in, and even work from, a bathtub filled with an herbal mixture that he used to calm the sores.