Intraoperative motor evoked potential monitoring to patients with preoperative spinal deficits: judging its feasibility and analyzing the significance of rapid signal loss.

BACKGROUND CONTEXT

Transcranial motor evoked potential (MEP) monitoring has been widely adopted in spine surgery, but so far the useful monitoring data for patients with preoperative spinal deficits (PPSDs) are limited. Originally we thought that they seemed technically more difficult and less reliable in performing the MEP monitoring to PPSDs.

PURPOSE

Our objective was to study (1) the feasibility of MEP monitoring in PPSDs and the (2) the significance of rapid MEP loss.

STUDY DESIGN/SETTING: A retrospective case notes study from a prospective patient register was used as the study design.

PATIENT SAMPLE

A total of 332 PPSDs who underwent posterior spine surgery with a reliable MEP monitoring were collected between September 2010 and December 2014.

OUTCOME MEASURES

Relevant MEP loss was identified as rapid amplitude reduction (more than 80% MEP) associated with high-risk surgical maneuvers or high-risk diagnoses.

METHOD

The muscles with higher strength were used to record the optimal MEP signal. MEP monitoring of these patients was considered to be feasible if reproducible signals had been obtained; moreover, sensitivity, specificity, positive predictive value (PPV), and negative predictive value were computed. The significance of the patients with rapid MEP loss was analyzed.

RESULTS

From a total of 332 PPSDs, 27 cases showed significant MEP loss (23 true positive, 4 false positive), and 21 showed new spinal deficits. Invalid MEP baselines were found in 11 paralysis and 6 severely incomplete paraplegia patients, and success rate of reliable MEP was 95.1% in PPSDs. The congenital kyphoscoliosis, tuberculous kyphoscoliosis, and thoracic spinal stenosis are considered high-risk diagnoses to result in MEP loss. The sensitivity of intraoperative MEP monitoring was 100%, the specificity 98.7%, the positive predictive value 85.2%, and the negative predictive value 100%.

CONCLUSIONS

Intraoperative MEP monitoring is feasible for most of the PPSDs. The rapid MEP loss during high-risk diagnoses and complicated surgical procedures may indicate new spinal deficits.