Polymyositis (PM) is a type of chronic inflammation of the muscles (inflammatory myopathy) related to dermatomyositis and inclusion body myositis.

[1] The hallmark of polymyositis is weakness and/or loss of muscle mass in the proximal musculature, as well as flexion of the neck and torso.

The hip extensors are often severely affected, leading to particular difficulty in climbing stairs and rising from a seated position.

[2] 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.

[3] The features they found associated with an increased risk of cancer were older age, age greater than 45, male sex, difficulty swallowing, death of skin cells, cutaneous vasculitis, rapid onset of myositis (<4 weeks), elevated creatine kinase, higher erythrocyte sedimentation rate and higher C-reactive protein levels.

Several factors were associated with lower-than-average risk, including the presence of interstitial lung disease, joint inflammation/joint pain, Raynaud's syndrome, or anti-Jo-1 antibody.

[8] Diagnosis is fourfold: History and physical examination, elevation of creatine kinase, electromyograph (EMG) alteration, and a positive muscle biopsy.