Reduced neuromuscular transmission safety factor in multiple sclerosis.

Regional intravascular injections of d-tubocurarine (0.3 mg) were administered in the hands of 23 normal subjects and 19 patients with multiple sclerosis. The degree of neuromuscular block and rate of recovery were determined by measuring the amplitude of the first dorsal interosseus muscle action potential which was evoked periodically by trains of five stimuli (3 Hz each) to the ulnar nerve. In normal subjects, the first response to the train returned to its preinjection level after 20.0 +/- 8.5 minutes and the fifth response after 27.6 +/- 7.8 minutes. Multiple sclerosis patients showed a significantly delayed recovery of the first response (58 percent of patients) and of the fifth response (42 percent), suggesting a latent defect of neuromuscular transmission.