Polymyositis

A rare idiopathic inflammatory myopathy (IIM) historically characterized by symmetric proximal muscle weakness, elevated muscle enzymes (creatine kinase), myopathic findings on electromyography, and muscle biopsy showing endomyial infiltration composed mainly of macrophages and lymphocytes. The features are non-specific, thus the disease should be distinguished from similar entities with specific clinical, immunological, histological features, notably dermatomyositis, immune-mediated necrotizing myopathy, anti-synthetase syndrome, inclusion body myositis, and myositis associated with other connective tissue disorder.