EFFECTS OF LOCAL INJECTIONS OF BOTULINUM TOXIN ON ELECTROPHYSIOLOGICAL PARAMETERS IN PATIENTS WITH HEMIFACIAL SPASM - ROLE OF SYNAPTIC ACTIVITY AND SIZE OF MOTOR UNITS

Ten patients with typical hemifacial spasm were examined before and af ter treatment with local injections of botulinum toxin type A. After a mean follow-up period of 38 days there was a reduction of the compoun d muscle action potential (CMAP) of the injected orbicularis oculi mus cle of 40%. Ephaptic transmission studied by selective stimulation of facial nerve branches revealed a preserved delayed response of the aff ected mentalis muscle. However, no delayed response could be recorded in the injected orbicularis oculi muscle in nine patients. The discrep ancy between complete loss of the delayed (ephaptic) response and only moderate reduction of the CMAP amplitude of the direct response may b e explained by preferential uptake of botulinum toxin type A by hypera ctive synapses involved in ephaptic transmission.