Dermatomyositis

Synonyms

Polymyositis, purple diseaseDermatomyositis is an inflammatory disease of the skin and skeletal muscle. In addition, organs such as the kidney or liver can be affected. Dermatomyositis is also called purple disease, as it is primarily noticeable by a purple redness in the area of the eyelids.

Frequency distribution

In dermatomyositis there are two phases in which the disease occurs. On the one hand, it can occur in childhood between five and 14 years of age. Approximately 0.2/100.

000 inhabitants/year are affected. More often, however, the disease occurs between the ages of 35 and 65, here mostly as a result of or before a tumour disease. The incidence is 0.6-1.0/100,000,000 inhabitants/year. Dermatomyositis is therefore a very rare disease, with women being affected more often than men. Most diseases manifest themselves in women at the age of 50, usually with a predisposition to tumour diseases.

Causes

The exact cause (etiology) of the disease is not yet clear. It is assumed that it is an immunological disease. This means that the body produces autoantibodies directed against a structure of the body.

In dermatomyositis, the body produces autoantibodies against a specific structure found in skin and bones, namely collagen. Collagen is a protein that is found in our connective tissue and ensures that our skin is elastic and yet mechanically resilient. At the same time, it provides great stability in the bones and yet ensures a certain flexibility.

In addition to skin and bones, collagen is also found in the structure of teeth, cartilage, tendons and various ligaments. Collagen is therefore a “universal protein” with many different subtypes that fulfil their characteristic function in the respective tissue. In the tendons, for example, collagen is arranged in parallel and thus has an enormous tensile force.

In the skin, the collagen is cross-linked to ensure high elasticity. Since in dermatomyositis, antibodies are directed against components of collagen, it is also called collagenosis. It is assumed that psychological stress, a genetic predisposition and exposure to sunlight support the development of such collagenosis.

Since collagen is found in every connective tissue and every organ, every organ can be affected. However, there are also cases that are restricted to the muscles or skin. If only the muscle is affected and no other organ or connective tissue, this is called polymyositis.

It is important to know that dermatomyositis is usually accompanied by a tumour, i.e. a neoplasia. In women, it is often cancer of the ovaries (ovarian carcinoma). It is not clear whether the cancer is the cause of the dermatomyositis or whether the dermatomyositis develops first and then a cancer develops.

Although the exact cause is not known, if dermatomyositis is present, one should always be tested for possible cancer. The situation is different for children who develop dermatomyositis. This is often a disease caused by viruses and almost always accompanied by muscle weakness. The viruses (presumably Coxsacki viruses) trigger an autoimmunisation, i.e. a defence reaction of the body to the body’s own collagen components.