Effect of spinal cord stimulation for thermal noxious stimulus pain threshold in Parkinson's disease

Background: Parkinson's disease (PD)-related pain or PD pain is a frequent non-motor symptom and is treated with pharmacotherapy and non-pharmacologic therapies such as deep brain stimulation (DBS) and spinal cord stimulation (SCS). The mechanism of PD pain relief by DBS is thought to involve increased pain threshold to nociceptive stimulation, whereas the mechanism of SCS has not been elucidated.Objective: PD pain relief by SCS may involve modulation of the pain thresholds in the spinal cord segments and supra-spinal actions. Therefore, we investigated the effect of SCS in patients who underwent SCS for intractable PD pain in the lower extremities by measuring pain thresholds to thermal nociceptive stimulation of the lower (leg) and upper (hand) parts of the stimulated spinal segment during SCS-off and SCS-on using quantitative sensory testing to determine the pain threshold.Methods: Seven PD patients with SCS in the lower thoracic spinal cord underwent measurements of cold sensory threshold, warm sensory threshold, cold pain threshold (CPT), and heat pain threshold (HPT).Results: In upper part of the stimulated spinal segment, CPT was significantly decreased during SCS-on compared to SCS-off (p < 0.01); whereas HPT was not significantly different. In lower part of the stimulated spinal segment, CPT was significantly increased during SCS-on compared to SCS-off (p < 0.05); and HPT was also increased (p < 0.05).Conclusion: This study shows that SCS raises the pain threshold to thermal nociception in PD patients. The primary mechanism of pain relief by SCS is thought to be segmental inhibition at the level of the stimulated spinal segments.