Patients with myasthenia gravis have been investigated with single fibre electromyography. In all myasthenic muscles recordings were obtained where there was an increase of the jitter and occasional blocking of different degree of single fibre action potentials. The jitter is the variability at consecutive discharges in the time interval between action potentials from two muscle fibres from the same motor unit. During prolonged activity the jitter increased and blockings occurred more and more frequently. The size of the jitter and the degree of blocking also depended on the discharge rate. At a low rate the jitter was lower and the degree of blocking less than at the high rate. Injection of edrophonium could decrease or increase the jitter or leave it unaffected. Single fibre electromyography is a sensitive way of studying the transmission in individual motor end-plates in myasthenia gravis and is also a valuable diagnostic aid.
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↵2 Address for correspondence: Dr Erik Stålberg, Department of Clinical Neurophysiology, University Hospital, S-750 14 Uppsala, Sweden.
↵3 Address for correspondence: Dr. Jan Ekstedt, Department of Neurology, University Hospital, S-750 14 Uppsala, Sweden.
↵1 This investigation was supported by the Swedish Medical Research Council (Grant no. 14 X-135).
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