Quantifying effects of spinal cord stimulation in chronic regional pain syndrome patients

Abstract

Background: Complex regional pain syndrome (CRPS) is a clinical disorder characterized by continuous, disproportionate pain and sensory, vasomotor, sudomotor and motor trophic changes. CRPS patients have a heterogeneous clinical picture caused by multiple underlying pathophysiology mechanisms including inflammation, vasomotor disturbances and central nervous system (CNS) dysregulation. Spinal cord stimulation (SCS) is believed to target multiple CRPS mechanisms by stimulating the dorsal column in the spinal cord. Closed-loop SCS is a recently developed form of SCS in which the stimulation intensity adapts to the patient's position, continuously stimulating the same amount of fibers in the dorsal column. This constant perceived stimulation intensity may benefit CRPS patients who are generally hypersensitive.

Objectives: To better understand the effects SCS has on the CRPS mechanisms, my research focuses on quantifying changes in vasomotor disturbances due to conventional SCS treatment using thermographic image analysis. In addition, exploratory analysis is performed in patients treated with closed-loop SCS to evaluate its effects on CRPS mechanisms.

Method: Various histogram features indicating temperature intensity were selected based on histogram distributions of the thermographic images. These features were then extracted from the affected and unaffected extremities of each image. The histogram features of patients with and without vasomotor improvement were compared based on the change in differences between affected and unaffected extremities after 3 months of SCS. The change between improved or not improved was then determined for different characteristics of the patients, such as affected extremity and CRPS type. It was hypothesized that with improved vasomotor symptoms, the affected and unaffected extremities would become more similar and thus the difference would become smaller.
For evaluation of the effects of closed-loop SCS on CPRS mechanisms, measurements were conducted before implantation and up to 6 months of follow-up. Measurements include thermographic images, CRPS severity score (CSS), Condition Pain Modulation (CPM), Temporal Summation (TS) and determination of sIL-2R levels using blood samples. In addition, conventional SCS was compared to closed-loop SCS, with patients randomized to receive both settings during the follow-up for two months.

Results: The following histogram features were selected: mean, median, minimum, maximum, peak, skewness, kurtosis, and quartile range. Based on 28 patients, for patients with improved vasomotor symptoms a decrease in difference was observed for histogram features mean, median, minimum, peak and quartile range. Furthermore, statistically significant differences were found in patients with vasomotor symptoms at baseline compared to patients without vasomotor symptoms for the mean (p=0.026), median (p=0.046), minimum (p=0.008), and quartile range (p=0.016). For patients with a cold CRPS type, statistically significant different feature values were observed between patients with and without vasomotor improvement in maximum (p=0.024), peak (p=0.016), and quartile range (p=0.027), with a decrease of histogram feature values. No statistically significant differences were found between the affected upper or lower extremities...