Modulation of somatosensory evoked potentials by various spinal cord stimulation modalities in a porcine model

Abstract

Tonic spinal cord stimulation (SCS), an advancement in the treatment of chronic pain, has been found to reduce somatosensory evoked potentials (SSEPs). Current literature lacks information regarding the effect on SSEPs of newer SCS modalities like burst and high-frequency (HF) SCS. My thesis addresses the current lack of understanding regarding various types of SCS and their effects on SSEPs. I used an anesthetized pig model to investigate the effect of tonic SCS, burst SCS, and HF SCS on SSEP waveform amplitude and latency. Additionally, I studied the effect of a novel type of SCS, ultra-low frequency (ULF), on SSEP amplitude and latency. SSEP waveform amplitudes and latencies were collected during each SCS modality and during washout periods between each SCS modality. SSEP amplitudes were significantly reduced for all 4 studied SCS modalities. The degree of this SSEP amplitude reduction was significantly larger between tonic SCS when compared to burst and ULF SCS. The majority of SSEP amplitude baselines were significantly different from each other. No significant changes were found to SSEP latencies during any of the SCS modalities. Most latency baselines between subjects were significantly different from each other. This project demonstrated the ability of a porcine model to act as an efficacious model for SCS research, due to its similar neural anatomy and compatibility with human stimulation devices. The results outlined above demonstrate that all four types of SCS significantly reduced SSEP waveform amplitudes in a porcine model, which typically signals dysfunction in the sensory pathway, but in the case of SCS application is suggested to be due to sensory transmission interference localized at the site of stimulation. The similar reductive effect on SSEP amplitudes observed across all four modalities suggests that they may have some mechanistic similarities in the way they affect somatosensory processing at the spinal, thalamic and cortical levels. The presence of outliers in the data is in line with clinical findings in which some patients are deemed non-responders to certain types of SCS. It remains to be seen if the effects on SSEPs by the four types of SCS in this study are correlated with successful pain relief. Future research should focus on mapping the inter- and intra-cellular communication that provides the mechanism for the pain relief that is observed during application of various SCS modalities.