The spectrum of electrophysiological abnormalities in Bell's palsy.

Background: As part of an investigation of a suspected "outbreak" of Bell's palsy in the Greater Toronto Area, a population-based sample of patients with Bell's palsy was investigated electrophysiologically to help understand the spectrum of abnormalities that can be seen in this setting.
Methods: Two hundred and twenty-four patients were surveyed, of whom 91 underwent formal neurological assessment. Of the latter, 44 were studied electrophysiologically using standard techniques. Thirty-two of the 44 patients fulfilled clinical criteria for Bell's palsy.
Results: A wide range of electrophysiological changes was observed. Blink responses were the most useful test showing diagnostic sensitivity of 81% and specificity of 94% compared to the contralateral control side. Needle electromyography was additionally helpful in only one patient of six with normal conduction studies.
Conclusions: There is a wide spectrum of electrophysiological abnormalities in Bell's palsy. Blink reflex latencies may be under-utilized in the assessment of the facial nerve in Bell's palsy. Facial EMG is not generally useful in routine assessment.