Somatosensory and motor evoked potentials in patients with tumours in the spinal canal.

Motor and sensory evoked potentials were recorded in 27 patients with expanding spinal tumour. The patients were divided into 2 groups: I. tumours at the level of the spinal cord and II. at the level of the cauda equina. On the basis of the localization of the tumour, midline and lateral subgroups were distinguished. The latencies of motor evoked potentials were prolonged in most of the patients, even those without paresis, in both groups. The motor evoked potentials detected subclinical motor lesions in 7 patients. All patients but one manifested sensory deficits, which could not be shown with the somatosensory evoked potentials. Significantly more prolonged cortical motor latencies were found in most of the patients with a laterally located tumour on the tumour side than contralaterally, whereas in somatosensory evoked potentials this difference was not apparent. On the basis of these observations, we concluded that motor evoked potentials, 1. could more reliably detect the neural deficit than somatosensory evoked potentials; 2. could show the side where the tumour was located; 3. proved useful in the detection of subclinical motor lesions. The general conclusion may be drawn that this electrophysiological method can provide useful information for the surgeon.