polymyositis

Polymyositis: description

When translating the term “polymyositis” from Greek into German, it becomes clear what causes the disease, namely inflammation (“-itis”) of many (“poly”) muscles (“myos”). It is counted among the rheumatic diseases and is considered an autoimmune disease, so based on a false reaction of the immune system.

The polymyositis is very similar to dermatomyositis, but in contrast to this only affects the muscles and not additionally the skin. Both polymyositis and dermatomyositis are often associated with other diseases, such as other autoimmune diseases, viral infections or cancer. However, a malignant tumor (malignancy) is less common in polymyositis patients than in those with dermatomyositis: in patients with polymyositis, malignancies are found about twice as frequently as in the normal population. In dermatomyositis, on the other hand, the risk is four times higher.

Who is affected by polymyositis?

Polymyositis, with an estimated 5 to 10 new cases per million people per year, is even rarer than dermatomyositis. In contrast to this, polymyositis is almost exclusively found in adults, children hardly develop it (juvenile polymyositis).

What are the symptoms of polymyositis?

The first symptoms of polymyositis, as with dermatomyositis, are often relatively nonspecific and include, for example, fatigue and a general feeling of weakness. Even fever is possible. Since such symptoms can also occur in many other diseases, starting with a common cold, they do not initially think of polymyositis.

On the other hand, it is characterized by progressive, symmetrical weakness of the muscles in weeks to months, especially in the pelvis, thighs, shoulders and upper arms. Muscle pain also occurs, but less often than with dermatomyositis. About one quarter to one half of all polymyositis patients also report joint pain.

As with dermatomyositis, other organs may be involved in polymyositis, including the heart and lungs, for example. Swallowing, respiratory and neck musculature can also be affected, which can result in swallowing disorders or respiratory problems, for example.

What is the cause of polymyositis?

The development of polymyositis is not explained in detail. It is known that in the affected person’s own immune system begins to proceed specifically against muscle cells (autoimmune reaction) – as well as in dermatomyositis. However, a closer look reveals that the mechanism of the autoimmune response in polymyositis is different than in dermatomyositis. In the case of the latter, so-called B-lymphocytes or the antibodies they produce are responsible for the damage to the muscles – indirectly: they damage small blood vessels in the muscles (and skin) and thus cause the typical symptoms. In polymyositis, on the other hand, there is direct damage to the muscle cells and not the blood vessels. In addition, this happens mainly through special T-lymphocytes (T-killer cells) – another “division” of the immune system.

What ultimately causes the immune system of polymyositis patients to suddenly attack the body’s own structures, is not yet clear. However, experts suspect that the misguided immune response is based on genetic predisposition and may be triggered by external influences such as infections.

In general, polymyositis does not always go the same way, but varies from patient to patient. The main symptom of muscle weakness is always one of them, but how strong the symptoms appear, at what intervals they decrease and increase, and how the disease progresses is very individual.

How is polymyositis diagnosed?

For the examination and diagnosis of polymyositis one resorts to the same methods as with dermatomyositis. An increase in certain laboratory values, conspicuous results in the electromyogram and imaging techniques such as ultrasound or MRI confirms the suspicion. The safe diagnosis finally provides the examination of a small muscle sample under the microscope. In the process, destroyed muscle cells and the accumulation of T lymphocytes in and between the muscle cells can be detected.

It must always be remembered that there are other diseases that can cause similar symptoms as polymyositis. In cases where only minor symptoms occur and the disease progresses slowly, it can be confused with other muscle diseases such as progressive muscular dystrophy. This refers to a group of hereditary muscle diseases whose main symptom is also a weakening of the muscles and that sometimes lead to death at a young age.

How is polymyositis treated?

The treatment of polymyositis takes place as with dermatomyositis with a drug suppression of the immune system. First, a shock therapy is performed with a glucocorticoid and then usually additionally used a drug from the group of immunosuppressants, for example, azathioprine or methotrexate. In addition, polymyositis and dermatomyositis patients are recommended to have special physiotherapy and specific muscle training. This is intended to prevent muscle atrophy and restriction of mobility.

Polymyositis: course and prognosis

Polymyositis is not easy to treat. The common drugs often have to be used for years and sometimes have strong side effects.

About half of the patients are able to stop the glucocorticoids within five years and are considered cured. However, the muscle weakness caused by polymyositis is often irreversible – a discrete, non-disabling weakness of the affected muscles may be left behind. In about 30 percent of cases, the therapy may bring the polymyositis to a standstill. In the remaining 20 percent, the disease progresses despite treatment.

In unfavorable cases, complications of the disease (especially in the area of ​​the lungs and heart) lead to death. Five years after the diagnosis “polymyositis “ 75 percent of patients still live, 55 percent after ten years.