Brief overview
- Definition: Polymyositis is a rare inflammatory muscle disease from the group of rheumatic diseases. It mainly affects adult women.
- Symptoms: Fatigue, general weakness, fever, muscle weakness (especially in the shoulder and pelvic area), muscle pain, joint pain, possibly other symptoms (e.g. difficulty swallowing, breathing problems, Raynaud’s syndrome, swollen gums)
- Causes: Autoimmune disease, the cause of which is not fully understood. Presumably genetic and triggered by external factors (such as infections).
- Diagnosis: Blood tests, electromyography (EMG), ultrasound, magnetic resonance imaging, muscle biopsy.
- Treatment: Medication (cortisone, immunosuppressants), physiotherapy and targeted muscle training.
- Prognosis: The right treatment can usually significantly alleviate or completely eliminate the symptoms. However, slight muscle weakness often remains. Complications and concomitant tumor diseases can worsen the prognosis.
Polymyositis: definition and frequency
The term “polymyositis” comes from the Greek and refers to an inflammation (“-itis”) of many (“poly”) muscles (“myos”). Polymyositis is one of the rheumatic diseases and is very similar to dermatomyositis. Unlike dermatomyositis, however, it only affects the muscles and not the skin.
Polymyositis occurs even less frequently than dermatomyositis, with around five to ten new cases per million people per year worldwide. It almost exclusively affects adults, usually between the ages of 40 and 60. Women are significantly more frequently affected than men.
Inclusion body myositis
For some time now, inclusion body myositis has been differentiated from polymyositis. This is an inflammatory muscle disease that mainly occurs in men over the age of 50. Inclusion body myositis causes the same symptoms as polymyositis, but develops more slowly. Unlike polymyositis, it does not affect any other organs and the muscle pain typical of polymyositis does not occur in inclusion body myositis.
There are also differences in the diagnostics. For example, muscle enzymes are not elevated in inclusion body myositis – in contrast to polymyositis. However, so-called inclusion bodies can typically be detected in the affected muscles during histological examinations (biopsies). These are small particles inside cells or cell nuclei that can be seen under a light microscope. They usually consist of defective proteins.
Polymyositis: Symptoms
As with dermatomyositis, the initial symptoms of polymyositis are often non-specific. They include, for example, fatigue and a general feeling of weakness. Fever is also possible. As such symptoms can also occur with many other illnesses (starting with a common cold), they do not initially suggest polymyositis.
However, they are characterized by symmetrical muscle weakness that progresses over a period of weeks or months, particularly in the pelvis, thighs, shoulders and upper arms. Muscle pain also occurs, but less frequently than in dermatomyositis. Many polymyositis patients also report joint pain.
As with dermatomyositis, polymyositis can also involve internal organs. This can lead to dysphagia, cardiac arrhythmia, cardiac insufficiency and/or pulmonary fibrosis, for example.
Other possible symptoms include Raynaud’s syndrome (blue coloration of the fingertips) and swollen gums.
In general, the course of polymyositis varies from patient to patient. The main symptom of muscle weakness always occurs. However, how severe the symptoms are, how quickly they progress and how severe the disease is overall is very individual.
Can polymyositis be cured?
In 30 percent of patients, treatment can bring the polymyositis to a halt. In 20 percent of patients, the treatment does not work and the disease progresses.
Risk factors for severe progression
Polymyositis is often more severe in older patients and in male patients. The same applies if the heart or lungs are also affected. Concomitant cancer is also considered a risk factor for a severe course of polymyositis. Life expectancy can be reduced in such cases.
Polymyositis: causes
Exactly how polymyositis develops has not been conclusively clarified. However, it is undisputed that it is an autoimmune disease. This means that the immune system attacks the body’s own structures due to dysregulation – in the case of polymyositis, the muscles.
Dermatomyositis is also an autoimmune disease. However, a closer look reveals that the autoimmune reaction in polymyositis is different from that in dermatomyositis:
- In dermatomyositis, the antibodies produced by the so-called B lymphocytes are primarily responsible for the muscle damage – indirectly: they damage small blood vessels in the muscles (and skin) and thus cause the typical symptoms.
But why does the immune system of polymyositis patients suddenly fight the body’s own structures? There is (still) no conclusive answer to this question. However, experts suspect that the misdirected immune response is genetic and may be triggered by external influences such as infections.
Polymyositis: diagnosis
Polymyositis is diagnosed using the same examination methods as dermatomyositis:
- Blood tests: As with dermatomyositis, certain blood values are elevated (e.g. muscle enzymes, CRP, erythrocyte sedimentation rate) and autoantibodies are often detectable (such as ANA).
- Electromyography (EMG): Changes in electrical muscle activity indicate damage to the muscles.
- Imaging: Procedures such as ultrasound or magnetic resonance imaging (MRI) confirm the suspicion.
- Muscle biopsy: A sample of the affected muscle tissue taken under the microscope shows destroyed muscle cells. T lymphocytes, which accumulate between the muscle cells in polymyositis, are also visible.
Exclusion of other diseases
For a reliable diagnosis, it is important to rule out other diseases with similar symptoms (differential diagnosis). Especially if the symptoms are mild and the disease progresses slowly, polymyositis can easily be confused with other muscle diseases.
Polymyositis: Treatment
Like dermatomyositis, polymyositis is initially treated with glucocorticoids (“cortisone”). They have an anti-inflammatory effect and dampen immune reactions (immunosuppressive effect). Other immunosuppressants are added later, such as azathioprine, cyclosporine or methotrexate.
As with dermatomyositis, experts also recommend regular physiotherapy and targeted muscle training. This helps polymyositis patients to maintain their mobility and prevent muscle atrophy.
