Experimental study on the correlation between abnormal muscle responses and F waves in hemifacial spasm.

Abstract

OBJECTIVES: To investigate the correlation between abnormal muscle response (AMR) and F wave by establishing an animal model of hemifacial spasm (HFS). METHODS: Both demyelination in the main trunk of the facial nerve just distal to stylomastoid foramen and vascular compression were used to duplicate animal model of HFS in ten New Zealand white rabbits. AMR and F waves were elicited from the orbicularis oculi and mentalis muscles respectively by stimulating marginal mandibular branch of the facial nerve 6 weeks post-operatively. Correlation analyses were used to compare the relationship between AMR/M and F/M amplitude ratio and between the duration of AMRs and F waves. RESULTS: There was a linear correlation between the mean values of the AMR/M and F/M amplitude ratio (r=0.8602, p<0.01), which can also be found between the duration of AMRs and F waves (r=0.7702, p<0.01). DISCUSSION: Enhanced F waves and AMRs may have the same origin. The F wave can be regarded as a more direct index in the diagnosis pre-operatively, monitoring intraoperatively and follow-up post-operatively in patients with HFS.