Dynamic changes in nociception and pain perception after spinal cord stimulation in chronic neuropathic pain patients

OBJECTIVES: Patients with an implanted spinal cord stimulation (SCS) system for pain management present an opportunity to study dynamic changes in the pain system in a situation where patients are not stimulated (i.e., experiencing severe pain) compared to a situation in which patients have just been stimulated (i.e., pain-free or greatly reduced pain). The aims of this study were (1) to determine if there are differences in nociceptive withdrawal reflex thresholds (NWR-T) and electrical pain thresholds (EP-T) before and after SCS and (2) to establish if these differences are related to psychological factors associated with chronic pain.

METHODS: Seventeen volunteers with chronic neuropathic pain participated in the experiment. Electrical stimuli were applied in order to assess the NWR-T and the EP-T. Additionally, psychological factors (i.e. pain characteristics, depression, anxiety and disability indexes) were also recorded. The NWR-T and EP-T were assessed with the SCS system off (at least 8 h before the experiment), and then reassessed 1 hour after the SCS system was turned on.

RESULTS: Ongoing pain intensity ratings decreased (P=0.018) while the NWR-T increased (P=0.028) after the SCS was turned on, whereas no significant difference was found for EP-T (P=0.324). Psychological factors were significant predictors for EP-T but not for NWR-T.

DISCUSSION: The results of this study suggest that pain relief after SCS is partially mediated by a decrease in the excitability of dorsal horn neurons in the spinal cord.