Spinal Cord Stimulation for Intractable Pain Evaluated by a Collision Study Using Somatosensory Evoked Potentials: A Preliminary Report

Objective Appropriate stimulation of the dorsal column is required in order to achieve optimal control over pain by way of spinal cord stimulation (SCS). In this study, we objectively evaluated changes in somatosensory evoked potentials (SEPs) during a collision test in order to investigate whether paresthetic sensation or amount of pain reduction was correlated with the degree of dorsal column stimulation. Materials and Methods We studied 12 patients with intractable pain who underwent permanent SCS implantation. SEP collision was examined while recording the cortical SEP components elicited by posterior tibial nerve stimulation. A positive collision effect was observed when the SEP amplitude was clearly reduced by the SCS. Results Based on the SEP collision findings, the effects of SCS were classified into four patterns: positive collision with pain reduction (Type 1), positive collision without pain reduction (Type 2), negative collision with pain reduction (Type 3), and negative collision without pain reduction (Type 4). Type 1 was observed for well-known diseases in which SCS was very effective, whereas Type 2 was seen in poor candidates for dorsal column stimulation. Patients with poststroke pain exhibited various patterns including types 1, 2, and 3. One patient showed Type 4 patterning, and we recommended further SCS trials before the abandonment of SCS therapy for this patient. Conclusions We show that SEP collision is useful for evaluating the degree of dorsal column stimulation needed as well as in considering factors related to differences between responders and nonresponders to SCS therapy.