Diagnostic significance of MEP elicited by electrical and magnetoelectric stimulation in acute/subacute supratentorial lesions.

Motor evoked potentials (MEP) elicited by transcranial electrical and magnetoelectric stimulation were examined prospectively in a total of 122 patients with supratentorial tumorous and nontumorous lesions in an acute/subacute neurosurgical setting. All patients had a hemiparesis contralateral to the lesion. It was the aim of our study to define the diagnostic significance of MEP with respect to superficial and deep localization of the lesions. To achieve this goal, MEP findings were correlated with the clinical motor status defining two categories: correct with pathological MEP, and false-negative with normal MEP. On the whole, we found correct results in 108 of 122 patients (88.5%) with electrical stimulation, and in 67 of 75 patients (89.3%) with magnetoelectric stimulation. There were false-negative results in 4 (11.5%) and 8 (10.7%) cases, respectively. In particular, with electrical stimulation 14 of 65 (21.5%), and with magnetoelectric stimulation 8 of 43 (18.6%) superficial lesions were missed, whereas deep lesions were correctly assessed in every case by either stimulation technique. In conclusion, the diagnostic significance of MEP for assessment of superficial supratentorial lesions is limited with the methods applied in this study. Whether more refined techniques may provide different results in a similar setting remains to be proved.