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Polymyositis is a type of inflammatory myopathy, related to dermatomyositis and inclusion body myositis. Polymyositis means ‘many muscle inflammation’.
Polymyositis tends to become evident in adulthood, presenting with bilateral proximal muscle weakness, often noted in the upper legs due to early fatigue while walking. Sometimes the weakness presents itself by the person being unable to rise from a seated position without help, or inability to raise their arms above their head. The weakness is generally progressive, accompanied by lymphocytic inflammation (mainly cytotoxic T8 lymphocytes).
Polymyositis, like dermatomyositis, strikes females with greater frequency than males. The skin involvement of dermatomyositis is absent in polymyositis.
The cause is unknown, but seems to be related to autoimmune factors,[1] genetics, and perhaps viruses. In rare cases, the cause is known to be infectious, associated with the pathogens that cause Lyme disease, toxoplasmosis, and others.
It is hypothesized that an initial injury causes release of muscle auto antigen i.e subsequently taken up by macrophages and presented to CD4+ TH cells.Activated TH cells synthesize IFN-? that stimulate further macrophages and further inflammatory mediator release like IL-1 and TNF-a
Another important event in the Pathogenesis of Polymyositis is increased expression of MHC proteins by m/s cells.Auto-Ag is presented in association with MHC-I molecules on the surface of Myocytes and is recognized by CD4 cytotoxic T cells that subsequently initiate m/s destruction.[2] [3]
Diagnosis is fourfold, including elevation of creatine kinase, history and physical examination, electromyograph (EMG) alteration, and a positive muscle biopsy.
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