[A case of polymyositis presenting pregnancy with acute respiratory failure].

A 33-year-old pregnant woman developed respiratory difficulty with bilateral pleural effusion 31 weeks into gestation. On admission she had an elevated serum level of creatine kinase, but muscle weakness in the extremities was mild. After an immediate and successful Cesarean section, she developed respiratory failure and mechanical ventilation was required. The patient was diagnosed as having polymyositis from the limb muscle biopsy. She was treated with dexamethasone at a dose of 8 mg, methylprednisolone++, 1 g daily for three days, and then prednisolone 60 mg daily. One week later the serum level of creatine kinase was normalized and the patient was weaned from ventilator support. The dose of prednisolone was tapered 10 mg every week and she was discharged two months after delivery without prednisolone. A chest CT scan revealed no interstitial pneumonitis or aspiration pneumonia, so her respiratory failure seemed to be ascribable to polymyositis-related respiratory muscle weakness and pleural effusion. However, severe involvement of respiratory muscles without generalized marked muscle weakness is extremely rare, and pleural complications have usually been described in association with pulmonary parenchymal diseases. During the following two years polymyositis has not recurred in this patient and there have been no data indicative of other overlapping collagen diseases. Reports of polymyositis which occurred during pregnancy are rare, and the pathogenesis and clinical outcome of these patients need to be carefully investigated.