[Blink reflexes in hemifacial spasm with special reference to the synkinetic responses].

Blink reflexes were studied in 20 patients with hemifacial spasm. The latencies of R1 on the affected side was not different from that on the unaffected side in 10 patients who had no previous facial nerve block, but increased in 10 patients with experience of facial nerve block. Synkinetic responses (SR 1, SR 2 and SR 2 c) were observed by the simultaneous recording from the orbicularis oris muscle on the affected side. SR 1 were obtained in all patients (100%), but SR 2 in 18 patients (90%) and SR 2 c in 19 patients (95%). The mean latency of SR 1 was slightly longer than the mean latency of R 1. When the site of stimulation was moved along the eyebrow from the supraorbital nerve approaching to the stylomastoid foramen, the latencies of R 1 and SR 1 became shorter, but R 2 and SR 2 were suppressed with increased latency. Following local anesthesia (xylocaine) to the temporal branch of the facial nerve, SR 1 was abolished with preserved R 1, R 2 and SR 2. On the other hand, R 2 and SR 2 were abolished with preserved R 1 and SR 1 following xylocaine block to the supraorbital nerve. The result suggested that the afferent pathway of SR 1 is the facial nerve (antidromic conduction) and that of SR 2 is the trigeminal nerve. Ephaptic transmission of those antidromic and orthodromic impulses forming a reverberating circuit should be one of the etiological factors in hemifacial spasm.