Physiological abnormalities in hemifacial spasm studied during microvascular decompression operations.

Area of Science:

• Neurology
• Neurosurgery
• Electrophysiology

Background:

• Hemifacial spasm (HFS) is characterized by involuntary unilateral facial muscle contractions.
• The precise pathophysiology, particularly the role of facial nerve excitability, remains under investigation.

Purpose of the Study:

• To investigate the pathophysiology of hemifacial spasm using intraoperative electrophysiologic recordings.
• To evaluate the effect of microvascular decompression on abnormal facial nerve activity.

Main Methods:

• Electrophysiologic recordings were performed during microvascular decompression surgery for hemifacial spasm.
• Electrical stimulation of facial nerve branches was used to assess nerve signal propagation.
• Electromyography (EMG) recorded muscle responses, including the blink reflex.

Main Results:

• Stimulation of facial nerve branches induced 'lateral spread' of activity to non-stimulated muscles, indicating abnormal nerve signal transmission.
• High-rate stimulation (50 pps) facilitated this lateral spread, which persisted even after reducing the stimulation rate.
• The blink reflex amplitude also increased with high-rate stimulation.
• Microvascular decompression eliminated both the lateral spread and blink reflex abnormalities.

Conclusions:

• Hemifacial spasm may result from hyperexcitability of the facial motor nucleus.
• Facilitation of cross-transmissions between facial nerve neurons contributes to the pathophysiology of hemifacial spasm.
• Microvascular decompression effectively addresses the underlying electrophysiologic abnormalities.