Muscle fiber changes of the vastus medialis in rheumatoid patients.

To study the pathology of muscle atrophy in rheumatoid arthritis (RA), we examined the vastus medialis in rheumatoid patients histologically. The relationship of the findings to their ambulatory ability and long-term steroid therapy was investigated. The muscles of the RA patients were also compared with those of patients with osteoarthritis (OA). Specimens of the vastus medialis were collected from 29 knees of 23 patients with RA and 16 knees of 13 patients with OA during total knee arthroplasty. Muscle fibers were classified according to their type, and the ratio between the area of single type I and type II fibers as well as the ratio between the total area of these fibers was calculated. The total area of type II fibers in the RA group was significantly greater than in the OA group (P < 0.05). In the RA group, the mean proportion of the type II fibers relative to the total muscle fiber area tended to increase with the decline of ambulatory ability, while there was no such increase in the OA group. The proportion of type II fibers was increased significantly in RA patients on long-term steroid therapy when compared to those without therapy. In the ratio of the area of a single fiber, there was no clear relationship to ambulatory ability and long-term steroid therapy. It is considered that muscle atrophy in RA is not solely disuse atrophy, but also has a close relationship to steroid therapy and the pathology of the disease itself.