Risk factors for false positive transcranial motor evoked potential monitoring alerts during surgical treatment of cervical myelopathy.
METHODS
Retrospective consecutive series review.


OBJECTIVE
To examine performance of transcranial motor-evoked potential (TcMEP) monitoring in patients undergoing surgery for cervical myelopathy and potential risk factors for false positive alerts.


BACKGROUND
Although use of TcMEP monitoring has been increasing and has been specifically recommended in patients with cervical myelopathy, rates and risk factors for false positive alerts have not been established.


METHODS
Intraoperative neuromonitoring data for 52 consecutive patients undergoing surgery for cervical myelopathy were reviewed. All major TcMEP alerts were identified. Comprehensive demographic and clinical data, preoperative imaging studies, operative, and anesthesia records were reviewed.


RESULTS
Six of 52 patients (12%) experienced a major TcMEP alert consisting of sustained >80% loss of amplitude. There were no somatosensory-evoked potential (SSEP)-related alerts. In 2 cases, an intraoperative wake-up test was negative and in 3 cases, surgery was completed without a wake-up test and without recovery of TcMEP signals. No new postoperative neurologic deficits were observed in these patients. One patient with new postoperative weakness was correctly predicted by loss of TcMEP signals. No new deficit was observed in the remaining 46 patients. Statistical analysis revealed significantly higher body mass index (28.8 vs. 35.0; P = 0.032) and length of surgery (191 vs. 283 minutes; P = 0.019) in patients with false positive alerts.


CONCLUSIONS
In this series of cervical myelopathy patients, sensitivity and specificity of TcMEP for detection of clinically significant intraoperative cord injury were 100% and 90%, respectively. Sensitivity and specificity of SSEP were 0% and 100%, respectively. The positive predictive value of a TcMEP alert was 17%. Possible risk factors for false positive TcMEP alerts include obesity and increased length of surgery. This study supports superior sensitivity of TcMEP compared with SSEP monitoring but identifies a relatively high false positive rate even in a selected high-risk cervical myelopathy population when this modality is applied in practice.
Kim
David H
DH
Department of Orthopaedic Surgery, Tufts University Medical School, New England Baptist Hospital, Boston, MA, USA. dhkim@caregroup.harvard.edu
Zaremski
Jason
J
Kwon
Brian
B
Jenis
Louis
L
Woodard
Eric
E
Bode
Robert
R
Banco
Robert J
RJ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000502:physiology / Q000601:surgery*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods / Q000592:standards*; D012189:Retrospective Studies; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013118:Spinal Cord Diseases / Q000503:physiopathology / Q000601:surgery*; D050781:Transcranial Magnetic Stimulation / Q000379:methods / Q000592:standards*; D016896:Treatment Outcome