An Electromyographic and Histological Study of Muscles in Rheumatoid Arthritis

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Abstract
Summary Electromyographic investigation and subsequent muscle biopsy were taken on 50 patients with verified rheumatoid arthritis in most cases from the m. biceps brachii. In 8 patients (16 %) the electromyogram showed signs of myogen involvement, especially a decrease in potential duration, whilst in the remaining 42 the mean duration was just below normal. In only 3 patients was spontaneous activity found at rest. 36 patients (72 %) presented microscopic changes at biopsy mainly in the form of myositis interstitialis nodularis. 9 of these patients (18 %) showed involvement of the muscle fibres. Compared with the 8 patients displaying a myogen electromyogram good agreement was found between the electromyographic and the microscopic pictures. No relation was seen between the pathologic findings (neither electromyographic nor microscopic) and the age, sex, duration of disease, and treatment, especially steroid treatment. It is concluded that rheumatoid arthritis can be complicated by myositis, in severe cases giving rise to involvement of the muscle fibres, and then presents a myogen pattern on the electromyogram. In a few cases, myositis can become inactive and leave a picture similar to that of muscular dystrophy.

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