[Motor-evoked potentials following electric and magneto-electric stimulation: the value and a comparison of both...

Motor evoked potentials (MEP) were recorded in a total of 145 patients with supratentorial (N = 29), infratentorial (N = 25) and spinal (N = 91) lesions affecting the descending pathways. In all cases potentials were evoked by electrical, in addition in 55 of them by electromagnetic stimulation of the motor cortex. The peripheral conduction time was determined in all patients by electrical stimulation of the cervical and lumbar nerve roots, respectively. This study was designed to compare both stimulation techniques (electrical vs. electromagnetic) regarding their significance in recording of potentials as well as in correlation of potentials with the motor status as established by clinical examination. Our results show that potentials were obtained in 87.6% following central (cortex) and in 100% following central electromagnetic stimulation. 87.9% of the recordings in infratentorial and spinal lesions show a correct and 12.2% a "false positive" correlation with the clinical motor status. On the other hand, the correlation was false negative in 13.8%, correct in 79.3% and "false positive" in 6.9% of the supratentorial cases. There was no difference between electrical and electromagnetic stimulation regarding diagnostic significance of potentials. Our results allow the following conclusions: both electrically and electromagnetically evoked potentials are sensitive for electrophysiological assessment of infratentorial and spinal lesions, but unreliable in evaluation of supratentorial lesions, especially in the acute stage. Due to its painlessness, electromagnetic stimulation is the method of choice for transcranial eliciting of MEP in the awake patient, who is capable of facilitation by voluntary background contraction of the target muscle.(ABSTRACT TRUNCATED AT 250 WORDS)