Single-fiber electromyography in myasthenia gravis
Single-fiber EMG studies were performed 106 times in the extensor digitorum communis muscles of 68 patients with myasthenia gravis. The patients were in various stages of treatment, usually with high doses of corticosteroids. In each study the overall mean jitter, the proportion of fibers with normal neuromuscular transmission, and the proportion of fibers showing blocking were determined. Abnormalities in each of these parameters correlated with the severity of clinical weakness. Five studies were normal by all criteria; two of these were in patients clinically in remission, and three were in patients having purely ocular myasthenia. Serial studies in 22 patients frequently correlated well with changes in clinical weakness, especially when the intervals between consecutive studies were longer than one month. The authors have found single-fiber EMG techniques to be of great value in confirming and quantitating the defect of neuromuscular transmission in myasthenia gravis, and in providing objective evidence of changes in neuromuscular blockade that may be too subtle to be demonstrated by other means.