[Electrophysiological testing in spinal cord tumors]

Evoked potentials (EPs) are useful to evaluate the functional impairment of motor and somatosensory pathways in spinal cord tumors. Conduction through pyramidal tracts is evaluated by motor EPs (MEPs) elicited by transcranial stimulation, magnetic for awake patients or electric in the operating room. Somatosensory EPs (SEPs) and laser EPs (LEPs) are complementary procedures to explore conduction in dorsal columns and spinothalamic tracts, respectively. MEPs as well as SEPs show conduction abnormalities in about 60% of cases with a sensitivity that increases up to 70% when both procedures are carried out. Abnormalities are observed in the absence of any clinical sign in respectively 7% and 15% of cases for MEPs and SEPs. Multilevel stimulations for SEPs recordings permit to detect segmental dysfunction in 70% in case of cervical TIM, even in the absence of clinical signs. LEPs are useful in specific clinical situations: they allow a dermatomal stimulation and are correlated to segmental thermoalgic anaesthesia. Electrophysiological testing plays an important role in the diagnostic and therapeutic strategy: before surgery, MEPs and SEPs objectively evaluate the functional impairment directly related to the lesion. They also help by permitting a follow-up, either before surgery when the surgical decision is delayed because of a good clinical tolerance of the lesion, or after operation to evaluate the functional evolution. Intraoperative monitoring of MEPs and SEPs allows informing the surgeon about the impact on each surgical manipulation. No prospective randomized study has been performed to date to compare clinical evolution after surgery with or without monitoring. Nevertheless, a wide consensus became established in favor of monitoring to limit the risk of postoperative definite deficit and to permit an optimal surgical resection without risk when responses are preserved.