The effects of botulinum toxin A on ephaptic transmission in idiopathic hemifacial spasm.

OBJECTIVE: Lateral spreading and synkinetic responses of blink reflex are a sign of ephaptic transmission in idiopathic hemifacial spasm (HFS). The aim of this study was to evaluate the effect of botulinum toxin A (Btx A) on ephaptic transmission in idiopathic HFS. METHODS: Thirty-three patients with idiopathic HFS were investigated. Btx A was injected only into the affected orbicularis oculi (OC) muscle. Electrophysiological studies were performed before and three weeks after the Btx A injection. RESULTS: After Btx A, the latencies of motor response and blink reflexes elicited from the OC muscle were significantly increased. The lateral spreading was not obtained in the OC muscle, while the orbicularis oris muscle response was not changed. There were no significant differences in the synkinetic responses of blink reflex. During needle EMG examination, positive sharp waves and fibrilation potentials were observed due to chemodenervation only in the OC muscle. CONCLUSION: Btx A affects only the neuromuscular junctions of the injected muscle and has no effect upon ephaptic transmission.