Conventional-SCS vs. Burst-SCS and the Behavioral Effect on Mechanical Hypersensitivity in a Rat Model of Chronic Neuropathic Pain: Effect of Amplitude

Objective: Various spinal cord stimulation (SCS) modes are used in the treatment of chronic neuropathic pain disorders. Conventional (Con) and Burst-SCS are hypothesized to exert analgesic effects through different stimulation-induced mechanisms. Preclinical electrophysiological findings suggest that stimulation intensity is correlated with the effectiveness of Burst-SCS. Therefore, we aimed to investigate the relation between amplitude (charge per second) and behavioral effects in a rat model of chronic neuropathic pain, for both Conventional Spinal Cord Stimulation (Con-SCS) and biphasic Burst-SCS. Materials and Methods: Animals (n=12 rats) received a unilateral partial sciatic nerve ligation, after which they were implanted with quadripolar electrodes in the epidural space at thoracic level 13. Mechanical hypersensitivity was assessed using paw withdrawal thresholds (WTs) to von Frey monofilaments, at various SCS intensities (amplitudes) and multiple time points during 60 minutes of stimulation and 30 minutes post stimulation. Results: Increasing amplitude was shown to improve the efficacy of Con-SCS, whereas the efficacy of Burst-SCS showed a nonmonotonic relation with amplitude. Con-SCS at 66% MT (n=5) and Burst-SCS at 50% MT (n=6) were found to be equally effective in normalizing mechanical hypersensitivity. However, in the assessed time period Burst-SCS required significantly more mean charge per second to do so (p<0.01). When applied at comparable mean charge per second, Con-SCS resulted in a superior behavioral outcome (p < 0.01), compared with Burst-SCS. Conclusion: Biphasic Burst-SCS requires significantly more mean charge per second in order to achieve similar pain relief, as compared with Con-SCS, in an experimental model of chronic neuropathic pain.