Facial motor evoked potential with paired transcranial magnetic stimulation for hemifacial spasm

Objective: Microvascular decompression (MVD) is widely considered the treatment of choice for hemifacial spasm (HFS), but not all patients immediately benefit from it. Numerous electrophysiological tests have been employed to monitor the integrity of the facial nerve prior to, during, and after MVD treatment. The authors sought to verify if facial motor evoked potential (FMEP) with paired transcranial magnetic stimulation (pTMS) can be utilized as a tool to predict prognosis following MVD for HFS.

Methods: FMEP using pTMS was performed preoperatively and postoperatively for 527 HFS patients who underwent an MVD treatment. Various interstimuli intervals (ISIs), which included 2, 10, 20, 25, 30, 75, and 100 msec, were applied for each paired stimulation and pTMS(%) was obtained. A graph of pTMS(%) versus each ISI was drawn for every patient and its pattern was analyzed in accordance with patients’ clinical outcomes.

Results: With ISIs of 75 and 100 msec, pTMS(%) was physiologically further inhibited, whereas it was relatively facilitated under ISIs of 20, 25, and 30 msec; loss of this specific pattern, that is, further inhibition-relative facilitation, indicated impaired integrity of the facial nerve. Those patients who immediately benefited from an MVD and experienced no relapse tended to show proper restoration of this further inhibition-relative facilitation pattern (p = 0.01). Greater resemblance between the physiological pattern of pTMS(%) and postoperative pTMS(%) was correlated to better outcome (p = 0.019).

Conclusion: FMEP with pTMS can be used as adjunctive tool in diagnosis of HFS and it may offer a significant improvement in predicting the prognosis of HFS following MVD.

Dr. Jae Sung Park is a neurosurgeon specializing in both functional neurosurgery and endovascular intervention.  He holds a PhD in neurosurgery from Sungkyunkwan University, Seoul, Korea as well as MD from Chung Ang University, Seoul, Korea.  He was employed by the Cleveland Clinic, Ohio, USA in 2007, followed by Ohio State University Hospital.  After working as a tumor/functional specialist in the US for two and a half year, he returned to his home country, South Korea, and became a professor at Konkuk University, School of Medicine. He is currently a tenured professor at Konyang University, Daejeon, Korea