Electrophysiological monitoring during CT-guided percutaneous cordotomy

During percutaneous cordotomy, impedance monitoring and electric stimulation have been widely used to enable a precise localization of the lesion electrode. The purpose of this study was to examine the possibility that the usage of additional electrophysiological techniques could help in improving the precision of the placement of the lesion electrode. Fourteen patients were monitored with 4 different techniques during CT-guided percutaneous cordotomy: 1) Median nerve somatosensory evoked potentials (mSEP): median nerve stimulation with recording from the scalp. 2) Spinal cord evoked potentials (SCEP): median nerve stimulation with recording via the cordotomy electrode. 3) Spinothalamic evoked potentials (SthEP): stimulation via the cordotomy electrode and recording from the scalp. Ipsilateral and contralateral mSEPs and SCEPs did not change after the lesion. SthEPs showed a significant decrease in 10 of 12 patients provided the stimulus intensity was kept below that producing a motor response (approx 0.5-1 mA). There was no obvious relationship between changes of the evoked potentials and the clinical outcome of the cordotomy. Our results suggest that there may be a relationship between the extent of the lesion and the decrease of the spinothalamic evoked potentials.