Pathogenesis (disease development)
The exact causes of polymyositis have not yet been determined. What has been proven so far are genetic factors (HLA associations) and pathologic autoimmunologic processes, meaning that the body’s immune system attacks myocytes (muscle cells). In contrast to dermatomyositis, in which antibodies cause myositis (muscle inflammation) by damaging the small blood vessels, polymyositis causes direct damage to the myocytes. T lymphocytes (killer T cells) are involved.
Etiology (causes)
Biographic causes
- Genetic burden – clustered occurrence of the HLA-B8 and HLA-DR3 haplotypes.
If autoimmune disposition is present, the following provoking factors (triggers) may be considered:
- Muscle strain
- Viral infections (coxsackie, picorna viruses).
- Medications (rare):
- Allopurinol (urostatic drug/for treatment of elevated uric acid levels).
- Antimalarials such as chloroquine
- D-penicillamine (antibiotic)
- Interferon alpha (antiviral and antitumor effects).
- Procainamide (local anesthetic)
- Simvastatin (statins; lipid-lowering drugs)
- If necessary, others, see under differential diagnoses / drugs.
