The lack of re-test reliability in human facial nerve neuromyography

Facial neuromyography is an objective electrophysiologic measurement used t o assess prognosis for recovery from facial paralysis. In the present study variability over time of the amplitude ratio in healthy subjects was inves tigated. Twenty healthy subjects underwent four neuromyographic tests at in tervals of one week. The study group consisted of 12 males and 8 females. A g es ranged from 23 to 36 years. The stimulation intensity required for sup ramaximal stimulation was 14.6 mA on average. The mean of the intraindividu al side-to-side difference of the evoked compound action potential was 32.5 %. Results of the four repeated rests ranged from no to 80% side-to-side di fferences in the same individual. The hypothesis of symmetrical evoked faci al compound potentials was nor supported by our data. As with previous inve stigators we found significant side-to-side differences in healthy subjects . Furthermore,we could also show for the first time that the amplitude rati o was not constant in every individual at repeated measurements. We conclud e that there is a physiological Variability that must be ta ken into accoun t in the interpretation of facial nerve neuromyography.