title: Analysis of facial motor evoked potentials for assessing a central mechanism in hemifacial spasm.
abstract: OBJECTIVE Hemifacial spasm (HFS) is a cranial nerve hyperactivity disorder characterized by unique neurophysiological features, although the underlying pathophysiology remains disputed. In this study, the authors compared the effects of desflurane on facial motor evoked potentials (MEPs) from the spasm and nonspasm sides of patients who were undergoing microvascular decompression (MVD) surgery to test the hypothesis that HFS is associated with a central elevation of facial motor neuron excitability. METHODS Facial MEPs were elicited in 31 patients who were undergoing MVD for HFS and were administered total intravenous anesthesia (TIVA) with or without additional desflurane, an inhaled anesthetic known to centrally suppress MEPs. All measurements were completed before dural opening while a consistent mean arterial blood pressure was maintained and electroencephalography was performed. The activation threshold voltage and mean amplitudes of the MEPs from both sides of the face were compared. RESULTS There was a significantly lower mean activation threshold of facial MEPs on the spasm side than on the nonspasm side (mean ± SD 162.9 ± 10.1 vs 198.3 ± 10.1 V, respectively; p = 0.01). In addition, MEPs were also elicited more readily when single-pulse transcranial electrical stimulation was used on the spasm side (74% vs 31%, respectively; p = 0.03). Although desflurane (1 minimum alveolar concentration) suppressed facial MEPs on both sides, the suppressive effects of desflurane were less on the spasm side than on the nonspasm side (59% vs 79%, respectively; p = 0.03), and M waves recorded from the mentalis muscle remained unchanged, which indicates that desflurane did not affect the peripheral facial nerve or neuromuscular junction. CONCLUSIONS Centrally acting inhaled anesthetic agents can suppress facial MEPs and therefore might interfere with intraoperative monitoring. The elevated motor neuron excitability and differential effects of desflurane between the spasm and nonspasm sides support a mechanism of central pathophysiology in HFS. Clinical trial registration no.: B2012:099 ( clinicaltrials.gov ).
authors.affiliation: Section of Neurosurgery and.
authors.forename: Marshall F
authors.initials: MF
authors.lastname: Wilkinson
authors.affiliation: Department of Anesthesiology and Perioperative Medicine, Faculty of Medicine, University of Manitoba and Health Sciences Centre, Winnipeg, Manitoba, Canada.
authors.forename: Tumul
authors.initials: T
authors.lastname: Chowdhury
authors.affiliation: Department of Anesthesiology and Perioperative Medicine, Faculty of Medicine, University of Manitoba and Health Sciences Centre, Winnipeg, Manitoba, Canada.
authors.forename: W Alan
authors.initials: WA
authors.lastname: Mutch
authors.affiliation: Section of Neurosurgery and.
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Kaufmann
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000077335:Desflurane / Q000494:pharmacology*; D019054:Evoked Potentials, Motor / Q000187:drug effects* / Q000502:physiology; D005260:Female; D019569:Hemifacial Spasm / Q000209:etiology / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D008297:Male; D061145:Microvascular Decompression Surgery; D008875:Middle Aged; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology; D011446:Prospective Studies; D055815:Young Adult
chemical_list: D018685:Anesthetics, Inhalation; D000077335:Desflurane
keywords: EEG = electroencephalographic; EMG = electromyographic; HFS = hemifacial spasm; LSR = lateral spread response; MAC = minimum alveolar concentration; MEP = motor evoked potential; MVD = microvascular decompression; TIVA = total intravenous anesthesia; desflurane; facial motor neurons; functional neurosurgery; hemifacial spasm; microvascular decompression; motor evoked potentials