Walsh & Hoyt: Polymyositis and Dermatomyositis

Polymyositis is an inflammatory myopathy that affects striated skeletal muscle and, less commonly, cardiac muscle. The diagnosis of polymyositis is based on the presence of at least two of the following: 1. Proximal muscle weakness. 2. Elevated serum levels of muscle-associated enzymes such as creatine kinase, aldolase, and lactic dehydrogenase. 3. An active myopathic pattern on electromyography. 4. Inflammatory changes, often associated with necrosis, degeneration, and regeneration of muscle fibers, in a muscle biopsy specimen.