[A statistical analysis of the intervals between motor unit impulses in patients with myasthenia]

Motor unit (MU) potentials of m. triceps br. of healthy subjects and patients with myasthenia gravis were recorded during slight isometric contractions. MU potentials were visually identified, semi-automatically coded and automatically led in the digital computer. In myasthenia the mean frequency of the MU discharges and SD of the interspike intervals were higher than in healthy states, the difference being not great, but significant. The interspike interval hystograms of single MUs were unchanged (normal). So the disturbances in pattern of motoneurone activity in myasthenia were mild. Proserin raised the muscle contraction strength and normalized the interspike interval variability but did not lower the frequency of MU discharges. The increase of the frequency may be accounted for the reduction of Renshaw inhibition.