Polymyositis and Dermatomyositis Symptoms, Signs and Causes

Muscle weakness can progress for several weeks or months. However, for the clinical detection of muscle weakness, a minimum of 50% of the muscle fibers must be damaged (thus, the presence of muscle lethargy indicates progression of the myositis). Affected persons may found it difficult to lift their arms above shoulder level, to walk up the stairs, to rise from sitting.