Blink reflex in patients with hemifacial spasm. Observations during microvascular decompression operations

Area of Science:

• Neurology
• Neurosurgery
• Physiology

Background:

• The blink reflex is typically absent during surgical anesthesia with inhalation agents.
• Hemifacial spasm (HFS) patients exhibit an abnormal early blink reflex component (R1) on the affected side under anesthesia.

Purpose of the Study:

• To investigate the blink reflex changes in hemifacial spasm patients undergoing microvascular decompression (MVD).
• To assess the diagnostic utility of the R1 component in HFS during surgical procedures.

Main Methods:

• Electromyography (EMG) recorded mentalis muscle responses to supraorbital nerve stimulation.
• Facial nerve compound action potentials (CAP) were measured during MVD surgery.
• Stimulation of the zygomatic branch of the facial nerve was also performed.

Main Results:

• Before MVD, supraorbital nerve stimulation elicited orbicularis oculi and mentalis muscle contractions (R1 component) in HFS patients.
• Post-MVD, the blink reflex was abolished, and mentalis muscle responses to facial nerve stimulation were absent.
• Mean latencies for R1 and CAP were recorded, with CAP latencies at 7.5 ms +/- 1.4 ms.

Conclusions:

• The R1 component of the blink reflex is a reliable indicator of facial nerve irritation in HFS.
• Successful MVD surgery effectively eliminates the abnormal R1 response, confirming surgical efficacy.
• These findings support using the blink reflex to monitor facial nerve integrity during HFS surgery.