Etude electromyographique de la paralysie de Bell

Abstract

Twenty-five cases of Bell's facial palsy have been studied by stimulation electromyography. By this method it is possible to predict the prognosis in an apparently complete paralysis provided that a long duration stimulus which may exceed 1 msec is applied, and that the evoked muscle action potential is studied. The absence of visible muscular contraction in response to electrical stimulation of the nerve is not sufficient to ascertain that the denervation is complete, since in 5 such cases, we obtained an evoked muscle action potential. If an evoked muscle action potential appears 8 days after the onset of the paralysis, the prognosis is good in spite of the apparent inexcitability of the nerve. Only cases in which muscle action potentials cannot be evoked have a poor prognosis. This was observed in 3 patients. The statistical analysis of electrophysiological parameters studied here indicated that in most cases the duration of latency was in inverse proportion to the duration of the negative phase of the evoked muscle action potential. In fact, the sum of the mean latency and mean duration (7.08 msec) is almost the same as that of the control values (7.04 msec). Therefore, it may be stated that in Bell's palsy, there is no slowing of overall nerve conduction velocity, but rather a block of the fast-conducting nerve fibres.