Longitudinal Changes in Sensory Processing and Clinical Outcomes During Spinal Cord and Dorsal Root Ganglion Stimulation to Treat Chronic Pain: A Pilot Study

The analgesic mechanisms and neurophysiological effects of spinal cord stimulation (SCS) and dorsal root ganglion stimulation (DRGS) are poorly understood. In this pilot repeated-measures study, we used quantitative sensory testing (QST) and self-reported questionnaires to investigate the effects of these therapies in chronic pain patients from pre-implantation up to one-year post-implantation. Several studies have reported stimulation-induced effects on QST, potentially clarifying how neurostimulation affects the nervous system, which is poorly understood. This pilot study aimed to probe chronic stimulation-induced changes using a wide battery of static and dynamic QST assessments as a precursor to future, larger studies. We enrolled 33 chronic pain patients selected as candidates for SCS and DRGS at pre-implantation and at three intervals up to at least 12 months post-implantation, with 18 completing at least one post-implantation visit. At each visit, we evaluated static (pressure-pain and vibration sensitivity) and dynamic (temporal summation, conditioned pain modulation) QST measures and patients self-reported pain-related clinical outcomes. Subjects reported significant improvements in pain severity, pain interference, pain disability, sensory and affective pain indices, sleep interference, depression, and general health at all post-implantation timepoints, as well as non-significant improvements in anxiety and coping. QST results typically failed to reach statistical significance. However, non-significant trends were observed for various stimulation-induced physiological effects, notably including reduced temporal summation at the primary pain site that was not observed at a non-painful control site. This exploratory study demonstrates that SCS and DRGS produce meaningful therapeutic and clinical benefits up to at least one-year post-implantation and may modulate somatosensory processing. However, caution in extrapolating results is warranted due to appreciable attrition, heterogeneous patient population, and the lack of a control group. Additional studies will be necessary to evaluate whether clinical improvements are maintained beyond one year as well as confirm potential QST trends.