Polymyositis (PM) (synonyms: acute parenchymal myositis; genuine polymyositis; hemorrhagic polymyositis; idiopathic inflammatory polymyositis; idiopathic polymyositis; myositis universalis acuta infectiosa; polymyositis in collagenoses (overlap-group/overlap syndromes); polymyositis with pulmonary involvement); ICD-10 M33. 2: polymyositis) is an inflammatory systemic disease of skeletal muscle (poly: much; myositis: muscle inflammation; thus, inflammation of many muscles) with lymphocytic infiltration (invasion of T lymphocytes). If the skin is also involved, it is called dermatomyositis (see “Dermatomyositis”). Involvement of internal organs such as the heart, lungs, gastrointestinal tract (gastrointestinal tract) is also possible.The disease belongs to the collagenoses (chronic inflammatory autoimmune diseases of connective tissue).
Polymyositis is divided into the following forms (see also “Classification”):
- Idiopathic polymyositis (with no apparent cause).
- Polymyositis in malignant tumors (concomitant disease in cancer).
- Polymyositis with vasculitis (vascular inflammation) in childhood.
- Polymyositis with collagenoses (overlap-group/overlap syndromes).
Furthermore, special forms exist.
In contrast to dermatomyositis, polymyositis is less often associated with maglinomas (paraneoplastic polymyositis). Frequently, the carcinomas affect the gastrointestinal tract (gastrointestinal tract), female breast, ovaries (ovaries), uterus (uterus), lungs, prostate. Usually polymyositis heals after removal of the tumor.
Sex ratio: males to females is 1: 2.
Frequency peak: The disease occurs more frequently between the 40th and 60th year of life. Children very rarely develop polymyositis (juvenile polymyositis).
Polymyositis is a rare disease.
The incidence (frequency of new cases) of polymyositis is about 5-10 cases per 1,000,000 inhabitants per year.
Course and prognosis: In the course of polymyositis, myalgias (muscle pain) and movement restrictions occur. A causal therapy does not exist yet. Therapy is protracted, but often leads to an improvement in quality of life. With regard to idiopathic polymyositis, 50% of patients are considered cured after five years and are able to stop taking medication. However, muscle weakness often remains. In one-third of cases, the disease is brought to a standstill, and in the remaining 20%, the course is progressive. If internal organs such as the lungs and heart are also affected, polymyositis can lead to death in the worst case.
The 5-year survival rate is approximately 75% and the 10-year survival rate is 55%.
