Electromyographic Changes in Rheumatoid Arthritis

Abstract

Muscular wasting is a prominent feature of rheumatoid arthritis.The exact reason for this has never been adequately explained.The idea that it is merely secondary to joint involvement or to disuse does not fit the facts, for the wasting may be out of proportion to the joint involvement, and may be found in muscles around joints that retain a full range of movement.Muscle pain and stiffness are prominent features of rheumatoid arthritis, and, indeed, it is well known that such symptoms may precede joint involvement by many years.Histological changes in the muscles have been described by several workers, but it is now agreed that these changes are non-specific and certainly not diagnostic of rheumatoid arthritis.Curtis and Pollard (1940) found perivascular infiltration of lymphocytes in the muscles ; Steiner et al. (1946) performed muscle biopsies on seven cases of rheumatoid arthritis and found inflammatory lesions in every case, calling the lesion " nodular polymyositis."These findings have been confirmed by other workers, and, if the results are analysed, positive biopsies occur in 40-100% of cases, depending on the series.While the histological changes of polymvositis with necrosis are distinct from the nodular polymyositis of rheumatoid arthritis, it must be remembered that Steiner et al. also demonstrated various stages of degeneration and atrophy to be present in rheumatoid muscle.Recently the concept of polymyositis has attracted attention, and, while muscle-wasting and pain are the prominent features of the condition, joint symptoms and signs are frequent, and a rheuimatoid type of polyarthritis may also be present (Richardson, 1957 ;Pearson, 1959).Polymyositis may be a primary condition.but it is usually secondary to such conditions as thyrotoxicosis,