Tumors localized near the central sulcus may cause increased somatosensory evoked potentials

Median nerve somatosensory evoked potentials (SEPs) may be altered in patients with cerebral tumors. In rare cases cortical responses may be increased, but the significance of this finding remains unclear.

We investigated 3 patients in whom an epileptic seizure was the only neurological symptom of a cerebral tumor located near the central sulcus. We studied median nerve SEPs, motor evoked potentials in abductor digiti minimi muscle, and long-loop reflexes in abductor pollicis brevis muscle bilaterally. Two patients also underwent intraoperative neurophysiological monitoring.

All 3 patients presented with enlarged cortical SEPs on the side of the brain tumor. The responses increased further post-operatively, and the enhancement persisted in follow-up examinations up to 6 months after surgical tumor extirpation. Intraoperative monitoring documented a substantial increase of the enlarged potential N20-P22 during tumor removal in one patient, who also presented with an exaggerated long-loop reflex on the tumor side. Transcranial magnetic stimulation revealed unremarkable motor evoked potentials in all 3 patients.

Distinct mechanisms must be considered in order to explain both immediate and long-term changes of neuronal excitability leading to increased cortical SEPs.

Hyperexcitability of cortical neurons or insufficient cortical inhibitory mechanisms may be responsible for increased SEPs, which may serve as an epileptic marker in patients suffering from a tumor near the central sulcus.