One hundred sixteen patients, aged 8 to 82 years, with myasthenia gravis were treated with prednisone, 60 to 80 mg daily, until the onset of improvement, followed by lower-dose alternate-day therapy of several years' duration. Of all patients, 80.2% achieved either remission (27.6%) or marked improvement (52.6%). Moderate improvement occurred in 14.7%, and 5.2% showed no improvement. Increasing age correlated with a favorable outcome, but sex, duration of illness prior to treatment, severity and distribution of weakness at the time of onset of treatment, and presence of thymoma were not factors in the response to therapy.

One-hundred-sixty single-fiber EMG studies of the extensor digitorum communis muscle were performed on 127 patients with myasthenia gravis; 131 demonstrated defective neuromuscular transmission. Jitter determinations in the biceps, deltoid or frontalis muscles increased the diagnostic yield significantly. Evoked-potential EMG studies were abnormal in less than 50 percent of patients in whom they were performed. The most sensitive criterion of abnormality was the percentage of fibers with increased jitter; the sensitivity of the test was enhanced, however, if the mean jitter of the tested muscle was also used as a criterion of abnormality. Since increased jitter may also be seen in primary muscle and nerve disease, these disorders must be excluded by other means before diagnosing myasthenia gravis on the basis of the single-fiber studies.

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It is of interest to compare the electrophysiological properties of normal human skeletal muscle with those of other mammalian species. In the present investigation the spontaneous subthreshold activity at the myoneural junction has been studied, and the membrane constants of the muscle fibres have been determined. As did Dillon, Fields, Gumas, Jenden & Taylor (1955); and Creese, Dillon, Marshall, Sabawala, Schneider, Taylor & Zinn (1957), we also found that human intercostal muscles proved to be excellent preparations for studies in vitro. It will be shown that the electrophysiological properties of these muscles are rather similar to those of other mammalian species, except that the frequency of the miniature end-plate potentials (m.e.p.p.) is considerably lower, and the membrane resistance higher. METHODSDuring thoracotomy operations on eight patients of both sexes and with no known muscle disease, specimens of external intercostal muscle were removed from the 5th, 6th, or 7th intercostal space in the mid-axillary line. The muscles were carefully dissected so that the specimens contained both origin and insertion, with continuous periosteum. Immediately upon removal the specimens were placed in continuously oxygenated Tyrode solution and taken to the laboratory for dissection and study. As described by Creese et al. (1957), longitudinal fusiform bundles of fibres, with their fibrous origin and insertion intact, could be dissected under a binocular microscope. The isolated bundles were about 15 mm long and 0-2-0 5 mm in diameter. They were mounted in a bath kept constantly at 370 C.The composition of the bathing fluid was that used by Liley (1956) and it was oxygenated by bubbling 95% 02+ 5% C02 through it immediately before its introduction into the muscle bath. The bath held about 30 ml. of solution, which was changed continuously at a rate of about 500 ml./hr.The usual techniques were employed for intracellular recording with capillary glass