Do motor evoked potentials allow quantitative assessment of motor function in patients with spinal cord lesions?

Motor evoked potentials (MEP) were recorded in a total of 110 patients with tumorous (n=39) and non-tumorous (n=71) lesions of the cervical (n=59), thoracic (n=37) and thoracolumbar (n=14) spinal cord. In all cases MEP were elicited by electrical stimulations, and in 50 of them also by magnetoelectric stimulation, of the motor cortex. The peripheral conduction time was determined by electrical stimulation of the lumbar nerve roots. It was the aim of this study to determine whether 1. MEP are sensitive for detection of lesions along the spinal cord and 2. whether they allow quantitative assessment of motor function. To achieve this goal, we compared potential and clinical findings of our patients, each divided into seven categories. Our results clearly showed the high sensitivity of MEP for semi-quantitative evaluation of motor function, as there were no false negative results in our series. Moreover, unilaterally accentuated motor deficits correlated significantly with changes in MEP, which were affected more strongly on the corresponding side (Student's t-test, α=0.05). However, clinical and electrophysiological findings did not correlate in the quantitative evaluation of the motor status as established by variance analysis (F=0.52). There was no difference in results with respect to the electrical and magnetoelectric stimulation technique. Our results lead to the following conclusions. MEP are sensitive for semiquantitative evaluation of spinal motor function; however, MEP do not allow quantification of the clinical motor status. We hypothesize that MEP changes are related more closely to the type of spinal cord damage (demyelination vs axonotmesis) and the duration of disease than to the actual clinical motor function.