Pathophysiology of hemifacial spasm: II. Lateral spread of the supraorbital nerve reflex.

The blink reflex was examined in 62 patients with hemifacial spasm. The latency and amplitude of the early (R-1) component of the orbicularis oculi response were increased as compared with the contralateral, unaffected side and controls, p less than 0.001. On the affected side, all patients showed a synkinetic response in the mental muscle, and after-activity and late-activity was observed after the reflex response. These findings indicate lateral spread of impulses to other fibers in the facial nerve (ephaptic transmission) and autoexcitation of fibers. The increased latency indicates a slowing of the nerve conduction in the facial nerve, in keeping with pathologic findings of focal demyelination.