title: Polymyositis: a case history approach to the differential diagnosis and treatment.
abstract: A wide range of conditions can mimic polymyositis. Thus, diagnosing this condition can be a challenge. Although no single criterion is diagnostic of polymyositis, the following criteria have been proposed and widely used: (1) symmetric proximal muscle weakness; (2) characteristic violaceous rash on the hands, elbows, and knees; (3) increased muscle enzymes in the serum; (4) characteristic electromyographic findings (insertional activity, fibrillation potentials, motor unit potentials of increased frequency and decreased duration, and normal conduction velocity in nerves); and (5) muscle biopsy specimen with characteristic inflammatory and myopathic changes. Although polymyositis primarily involves muscle, up to 20% of patients may have extramuscular problems. The main treatment for polymyositis is high-dose corticosteroids. In corticosteroid-resistant patients, methotrexate is often effective. In this report, case histories are presented to highlight the usefulness and the limitations of the common diagnostic criteria for polymyositis.
authors.affiliation: Division of Rheumatology, Mayo Clinic, Rochester, MN 55905.
authors.forename: T W
authors.initials: TW
authors.lastname: Bunch
mesh_terms: D000305:Adrenal Cortex Hormones / Q000627:therapeutic use; D000328:Adult; D000368:Aged; D003937:Diagnosis, Differential; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008727:Methotrexate / Q000627:therapeutic use; D008875:Middle Aged; D009132:Muscles / Q000201:enzymology / Q000473:pathology; D009220:Myositis / Q000150:complications / Q000175:diagnosis* / Q000201:enzymology / Q000473:pathology / Q000628:therapy*
chemical_list: D000305:Adrenal Cortex Hormones; D008727:Methotrexate