Two cases of polymyositis associated with interstitial pneumonia with anti-OJ (isoleucyl tRNA synthetase) antibodies

We present two cases of polymyositis (PM) associated with interstitial pneumonia (IP) whose sera contain autoantibodies to OJ (isoleucyl tRNA synthetase). The first patient is a 51 year-old female who was diagnosed as rheumatoid arthritis (RA) and treated with gold and corticosteroid at another hospital. She was admitted to Keio University Hospital due to worsening of dyspnea on exertion and polyarthritis. Laboratory findings revealed elevation of serum CK and LDH. A diagnosis of PM was made based on the myogenic pattern of EMG and pathological feature by muscle biopsy. Chest radiography and CT showed interstitial fibrosis. Because of clinical deterioration, the dose of corticosteroid was increased (prednisolone 50 mg/day) and her symptom was stabilized. The second patient, a 62 year-old male, was admitted to Kawasaki Municipal Hospital because of dyspnea on exertion, polyarthritis, and fever. He was diagnosed as PM associated with IP on the basis of his clinical and laboratory findings, and chest radiography. He was treated with methylprednisolone pulse therapy (800 mg/day for three days) and his symptoms were improved. Both patients were found to have autoantibodies to the OJ. Autoantibodies to aminoacyl tRNA synthetase have been described to be associated with myositis and/or IP. In North America, it was reported that all patients with anti-OJ had either myositis or IP or both. This suggests that anti-OJ was commonly associated with the anti-synthetase syndrome observed with other anti-synthetases. This is the first report of Japanese patients with anti-OJ antibody. The clinical features of these patients were likely to be similar to those observed in North American patients. However, further studies are necessary to clarify the precise clinical significance of this antibody.