Electrophysiologic investigation during facial motor neuron suppression in patients with hemifacial spasm: possible pathophysiology of hemifacial spasm: a pilot study.
OBJECTIVE
To evaluate the pathophysiological mechanism of hemifacial spasm (HFS), we performed electrophysiological examinations, such as supraorbital nerve stimulation with orbicularis oris muscle recording and lateral spread tests, after suppressing the patient's central nervous system by administering intravenous diazepam.


METHODS
Six patients with HFS were recruited. Supraorbital nerve stimulation with orbicularis oris muscle recording and the lateral spread test were performed, followed by intravenous application of 10 mg diazepam to achieve facial motor neuron suppression. Subsequently, we repeated the two electrophysiological experiments mentioned above at 10 and 20 minutes after the patients had received the diazepam intravenously.


RESULTS
Orbicularis oris muscle responses were observed in all patients after supraorbital nerve stimulation and lateral spread tests. After the diazepam injection, no orbicularis oris muscle response to supraorbital nerve stimulation was observed in one patient, and the latencies of this response were evident as a slowing tendency with time in the remaining five patients. However, the latencies of the orbicularis oris muscle responses were observed consistently in all patients in the lateral spread test.


CONCLUSIONS
Our results suggest that ectopic excitation/ephaptic transmission contributes to the pathophysiological mechanisms of HFS. This is because the latencies of the orbicularis oris muscle responses in the lateral spread test were observed consistently in the suppressed motor neuron in our patients.
Department of Rehabilitation Medicine, Incheon St. Mary's hospital, The Catholic University of Korea College of Medicine, Incheon, Korea.
Soo In
SI
Choi
Department of Rehabilitation Medicine, Incheon St. Mary's hospital, The Catholic University of Korea College of Medicine, Incheon, Korea.
Min-Wook
MW
Kim
Department of Rehabilitation Medicine, Incheon St. Mary's hospital, The Catholic University of Korea College of Medicine, Incheon, Korea.
Dong Yoon
DY
Park
Department of Neurosurgery, Incheon St. Mary's hospital, The Catholic University of Korea College of Medicine, Incheon, Korea.
Ryoong
R
Huh
Department of Rehabilitation Medicine, Incheon St. Mary's hospital, The Catholic University of Korea College of Medicine, Incheon, Korea.
Dae-Hyun
DH
Jang
Blinking; Diazepam; Electromyography; Hemifacial spasm; Pathophysiology