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Efficacy of Biphasic Transcranial Electric Stimulation in Intraoperative Motor Evoked Potential Monitoring for Cervical Compression Myelopathy

Ukegawa, Dai MD; Kawabata, Shigenori MD, PhD; Sakaki, Kyohei MD, PhD; Ishii, Senichi MD, PhD; Tomizawa, Shoji MD, PhD; Inose, Hiroyuki MD, PhD; Yoshii, Toshitaka MD, PhD; Kato, Tsuyoshi MD, PhD; Enomoto, Mitsuhiro MD, PhD; Okawa, Atsushi MD, PhD

doi: 10.1097/BRS.0000000000000082
Cervical Spine

Study Design. Retrospective analysis of prospectively collected data from consecutive patients undergoing 2 methods of transcranial electrical motor evoked potential (TCE-MEP) monitoring during cervical spine surgery.

Objective. To investigate the efficacy of biphasic transcranial electric stimulation, the deviation rate, amplitude of TCE-MEPs, complications, and sensitivity and specificity of TCE-MEP monitoring were compared between the biphasic and conventional monophasic stimulation methods.

Summary of Background Data. With biphasic stimulation, unlike monophasic stimulation, measurement time can be reduced considerably because a single stimulation elicits bilateral responses almost simultaneously. However, no study has yet reported a detailed comparison of the 2 methods.

Methods. Examination 1: Amplitude and derivation rate of TCE-MEPs was compared for monophasic and biphasic stimulation in the same 31 patients with cervical compression myelopathy. Examination 2: Sensitivity, specificity, and complications of TCE-MEP monitoring were compared in 200 patients with cervical compression myelopathy who received monophasic or biphasic stimulation (100 patients each) during intraoperative monitoring.

Results. Examination 1: Derivation rates of biphasic stimulation in the deltoid, biceps brachii, abductor digiti minimi, and flexor hallucis brevis muscles were the same or higher than for monophasic stimulation. TCE-MEP amplitudes elicited by biphasic stimulation compared with monophasic stimulation were significantly larger in the biceps (paired t, P < 0.0001), but similar in the other 3 muscles. Examination 2: In the biphasic and monophasic stimulation groups, warnings were issued to surgeons in 10 and 11 cases, for a sensitivity of 100% for both groups and specificity of 97.8% and 96.7%, respectively. No complications related to stimulation were observed in any of the 200 patients.

Conclusion. Biphasic stimulation had similar or higher derivation rates and equivalent sensitivity and specificity than monophasic stimulation. No complications were observed for either stimulation method. Biphasic stimulation is an effective TCE-MEP monitoring method for cervical spine surgery that may also reduce measurement time.

Level of Evidence: 4

Supplemental Digital Content is Available in the Text.Amplitude, derivation rate, complications, sensitivity, and specificity were compared between biphasic and monophasic stimulation in transcranial electrical motor evoked potential (TCE-MEP) monitoring during cervical spine surgery. Biphasic stimulation showed equivalent results to monophasic stimulation. Biphasic stimulation was effective for TCE-MEP monitoring during cervical spine surgery and contributed to reducing measurement time.

Department of Orthopaedic Surgery, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, Tokyo, Japan.

Address correspondence and reprint requests to Shigenori Kawabata, MD, PHD, Department of Orthopaedic Surgery, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan; E-mail:

Acknowledgment date: October 15, 2012. First revision date: July 29, 2013. Acceptance date: October 12, 2013.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

The Ministry of Health, Labour and Welfare of Japan research grant funds were received, in part, to support this work.

Relevant financial activities outside the submitted work: payment for writing or reviewing the manuscript and grants/grants pending.

© 2014 by Lippincott Williams & Wilkins