ABSTRACT
BACKGROUND AND PURPOSE: Hemifacial spasm is clinically characterized by involuntary co-contraction of unilateral facial muscles innervated by facial nerve and presence of synkinetic response between facial muscles innervated by different branches of facial nerve is considered as the electrophysiological hallmark of this disease. We performed this study in order to analyse and thereby to approach the pathogenesis of these synkinetic responses in detail. METHODS: Blink reflex test was applied to the 21 patients with hemifacial spasm. With some modification of conventional blink reflex methodology, synkinetic responses between orbicularis oculi and orbicularis oris muscles were recorded on both affected and unaffected sides. RESULTS: Among 21 patients, 10( 47.6% ) showed synkinetic responses both on affected and unaffected side, 8( 38.1% ) only on affected side, and 3( 14.3% ) did not show any evidence of synkinesis on either side. CONCLUSION: These findings could be considered as additional supportive evidence that the facial neuronal hyperexcitability is working in hemifacial spasm as synkinesis on unaffected side cannot be explained solely by peripheral mechanism. Further research on change of synkinetic behavior after microvascular decompression surgery seems to be needed.