Facial F Waves And Ephaptic Abnormal Muscle Responsesin Hemifacial Spasm:Evaluation Of Pathophysiology And Effect Of Botulinum Toxim Therapy

Abstract

Two opposing views about generation of hemifacial spasm (HFS), based on axonoaxonalephaptic transmission and hyperexcitability of the facial motornucleus, stili exist. Our aims were to determine underlying mechanism with electrophysiological techniques and to investigate the effect of botulinum toxin (BTX) therapy on these electrophysiological parameters in HFS . We studied a group of 23 patients with HFS, including 4 patients with postparalytic HFS and 20 healthy controls . In 10 patients who treated with BTX, these investigations have been done about 1 month later. Abnormal muscle responses (AMR), exhibiting ephaptic transmission, have been shown in all patients except 2 patients with postparalytic HFS. F wave frequency and F/M amplitude ratio were significantly increased on the spasm side. After BTX injections, F/M amplitude ratio, F wave frequency and AMR/M amplitude ratio were decreased. Our fındings showed presence of both ephaptic transmission on facial nerve and hyperexcitability of facial moto-nucleus in HFS patients. We concluded that ephaptic transmission andhyperexcitability of facial moto-nucleus are important pathophysiologic factors in HFS .