Dermatomyositis is a chronic disease that affects the skin and muscles. It is an autoimmune disease whose origin is still unknown, classified in the group of idiopathic inflammatory myopathies, alongside for example polymyositis. The pathology evolves for years with a good prognosis, in the absence of serious complications, but can hamper the patient’s motor skills. It is estimated that 1 in 50 to 000 in 1 people live with dermatomyositis (its prevalence) and that the number of new cases annually is 10 to 000 per million population (its incidence). (1)

Symptoms of dermatomyositis are similar or similar to those associated with other inflammatory myopathies: skin lesions, muscle pain and weakness. But several elements make it possible to distinguish dermatomyositis from other inflammatory myopathies:

• Slightly swollen red and purplish patches on the face, neck and shoulders are usually the first clinical manifestations. The possible damage to the eyelids, in the form of glasses, is characteristic.
• The muscles are affected symmetrically, starting from the trunk (abdominals, neck, trapezius…) before reaching, in some cases, the arms and legs.
• The high probability of being associated with cancer. This cancer usually starts in the months or years after the disease, but sometimes as soon as the first symptoms appear (it also happens just before them). It is most often cancer of the breast or ovaries for women and of the lung, prostate and testes for men. Sources do not agree on the risk for people with dermatomyositis of developing cancer (10–15% for some, one-third for others). Fortunately, this does not apply to the juvenile form of the disease.

An MRI and muscle biopsy will confirm or deny the diagnosis.

Recall that dermatomyositis is a disease belonging to the group of idiopathic inflammatory myopathies. The adjective “idiopathic” meaning that their origin is not known. To date, therefore, neither the cause nor the precise mechanism of the disease is known. It would likely result from a combination of genetic and environmental factors.

However, we know that it is an autoimmune disease, that is to say causing a disruption of the immune defenses, autoantibodies turning against the body, in this case against certain cells of the muscles and skin. Note, however, that not all people with dermatomyositis produce these autoantibodies. Drugs could also be triggers, as could viruses. (1)

Women are affected by dermatomyositis more often than men, about twice as many. This is often the case with autoimmune diseases, without knowing the reason. The disease can appear at any age, but it is observed that it appears preferentially between 50 and 60 years. With regard to juvenile dermatomyositis, it is generally between 5 and 14 years old that it appears. It should be emphasized that this disease is neither contagious nor hereditary.

In the absence of being able to act on the (unknown) causes of the disease, treatments for dermatomyositis aim to reduce / eliminate inflammation by administering corticosteroids (corticosteroid therapy), as well as to fight against the production of autoantibodies to the by means of immunomodulatory or immunosuppressive drugs.

These treatments make it possible to limit muscle pain and damage, but complications can arise in the event of cancer and various disorders (cardiac, pulmonary, etc.). Juvenile dermatomyositis can cause severe digestive problems in children.

Patients should protect their skin from the sun’s UV rays, which would aggravate the skin lesions, by means of covering clothing and / or strong sun protection. As soon as the diagnosis is established, the patient should undergo regular screening tests for cancers associated with the disease.