Predictive value of somatosensory evoked potentials for long-lasting pain relief after spinal cord stimulation:: Practical use for patient selection

OBJECTIVE: Spinal cord stimulation (SCS) has been used for more than 30 years in patients with intractable neuropathic pain, and global success rates have varied from 40 to 70%, according to reported series. Patient selection is currently based on a preliminary percutaneous, test which is useful but invasive, increases the risk of infection, and has yielded false-positive and false-negative results. In this study, we evaluated an alternative method of predicting the effectiveness of SCS before deciding whether to implant laminotomy electrodes- specifically, assessment of neural conduction in the dorsal columns with the use of somatosehsory, evoked potentials (SSEPs). Thus; we examined, the value of preoperative central conduction time (CCT) of SSEPs to stimulation at the level of the painful area as a possible predictor of patient outcome after SCS. METHODS: Ninety-five patients were evaluated during a mean follow-up period of 18.8 months. Patients were classified into four categories according to the location of the lesion responsible for paim: 28 patients had lesions of the peripheral nerves, 27 had radicular lesions, 8 had root avulsions, ansd 32 had cord lesions. The SCS electrode was implanted through an interlaminar opening at the upper part of the painful territory without performing a percutaneous screening test. Clinical and social markers of pain relief (i.e., Visual Ana;log Scale scores, analgesic drug intake, work status) were evaluated prospectively 2 months after implantation and then annually. RESULTS: The global.success rate in our study group, with success defined as at least 50% long-term pain relief, was 54.7% (52, of 95 patients). Statistical analyses showed a clear influence of preopetative CCT on SCS outcomes. Thus, the success rate was nil in patients with significantly abnormal CCT, whereas it can was 75.4% in patients with normal preoperative SSEPs. Significant differences between the two groups of patients also were observed with regard to medication, intake and work status. CONCLUSION: Preoperative, SSEPs. provide an objective reduction of patient outcome after SCS. We suggest at if-a patient's CCT is abolished or significantly altered, the patient should not undergo SCS.