[Polymyositis after interferon beta treatment of chronic hepatitis type C].

We reported a case of polymyositis manifested after beta-interferon therapy for chronic viral hepatitis type C. In November 1992, a 62-year-old female was diagnosed as having chronic viral hepatitis type C. In January 1993, she was treated with beta-interferon(total 2.52 x 10(8)IU). In March 1993, after the treatment, she noticed weakness and atrophy of her lower extremities. Neurological examination revealed proximal dominant muscle weakness and atrophy of the extremities. Increased levels of serum CK and aldolase were disclosed on admission. By needle EMG, a low voltage with short duration interference pattern was noted. February 7, by muscle biopsy of the right quadriceps, necrotic myofibers, marked variation in fiber diameter, stromal mononuclear cell infiltration, and endomysial fibrosis was detected. The immunological stain of infiltrating cells in the muscle fibers revealed CD4:CD8 ratio as 64:55, whereas in conventional polymyositis CD8 cells dominate CD4 cells. Diagnosis of polymyositis was made and oral prednisolone 60 mg a day was started. Her symptoms and signs improved gradually and she was discharged after 2 months. Many adverse effects due to immunological disturbances caused by interferon treatment have been reported, but polymyositis due to interferon has been very rare. When interferon will be prescribed, manifestation of polymyositis should be considered.