A case of polymyositis complicated with myasthenic crisis.

We report a 62-year-old woman who suffered from polymyositis (PM) complicated with myasthenic crisis. Electromyography and muscle biopsy indicated a diagnosis of PM; however, respiratory failure due to respiratory muscle weakness was seen in spite of a normal serum creatine kinase (CK) level. The positive anti-acetylcholine receptor antibody led us to the diagnosis of myasthenic crisis. PM with respiratory muscle weakness is rare. We suggest that the possibility of other neurological disorder complications should be considered when PM patients have respiratory muscle weakness out of proportion to the serum CK level.