Duration, amplitude, and shape of muscle action potentials in poliomyelitis

Abstract

Durations, amplitudes and shapes of action potentials have been studied in paretic muscles of 48 cases of poliomyelitis which were partly followed from the acute stage of the disease in repeated examinations up to one year after the onset of paresis. Approximately one month after the onset of paresis in part of the muscles examined the distribution curves of action potential duration showed a displacement to higher values as compared with normal muscle. This increase is the more pronounced the more severe the impairment of the muscle and the longer the time elapsed after the onset of paresis. Comparing equally affected muscles, a significant increase in duration was found only in those which one year later did not show any improvement of function. Corresponding with findings in muscular atrophies caused by other spinal lesions, in poliomyelitic muscle a correlation existed between the degree of impairment, the occurrence of synchronous activity between different regions of the same muscle, and the increase in mean duration of the action potentials. In both severely and moderately affected muscles the mean amplitude of the action potentials exceeded significantly that of normal muscle. This increase was already present a few days after the onset of paresis. The rapid decrease in the amplitude of the action potentials which characterizes fatigue in voluntary effort of paretic muscles in poliomyelitis, has been observed in some cases in the acute stage of the disease. Paretic muscles from poliomyelitis showed an increase in the occurrence of polyphasic action potentials — especially grouped action potentials — as compared with normal muscle, though they occur less frequently than in muscular atrophies caused by other spinal lesions. Similarly fibrillation action potentials were less frequently observed in poliomyelitic muscle (18 per cent of muscles examined) than in other muscular atrophies of spinal or peripheral neurogenic origin (35 per cent of muscles examined).