Hemifacial spasm: an electrophysiological evidence of facial motorneurons hyperexcitability.

Twenty patients with primary hemifacial spasm and ten patients with Parkinson's disease were studied by means of paired stimuli blink reflex. The second stimuli were delivered at a varying time interval between 50-900 ms. The R2 response's absolute refractory periods were compared between patients and twenty one age-matched normal controls as well as between hemifacial spasm and Parkinson's disease. In normal subjects, the mean absolute refractory period was found to be 271.42 +/- 64.36 ms, in hemifacial spasm 160.00 +/- 50.62 ms and in Parkinson's disease 157.14 +/- 53.45 ms. The absolute refractory periods obtained from patients were significantly shorter than in normal controls (p < 0.05). However the values between patients with hemifacial spasm and Parkinson's disease were not (p > 0.05). This result strongly supports bilateral facial motoneurons hyperexcitability as the underlying mechanism of hemifacial spasm.