The impact of obesity on the effectiveness of spinal cord stimulation in chronic spine-related pain patients.

BACKGROUND CONTEXT: Chronic pain and obesity are both on the rise. Spinal cord stimulation has gained increasing popularity in the pain management field for the treatment of spine-related chronic pain, however to-date, the correlation between the spinal cord stimulator effectiveness and increasing body mass index (BMI) has not been fully established. PURPOSE: We aimed to investigate the correlation between patients' BMI and the percentage of pain relief as well as opioid utilization in chronic spine-related pain patients treated with spinal cord stimulation. STUDY DESIGN: Retrospective cohort study. PATIENT SAMPLE: Patients with chronic spine-related pain who were treated with a spinal cord stimulator. OUTCOME MEASURES: Eleven-point numeric rating scale for pain and opioid utilization. METHODS: Following Institutional Review Board approval, data from all eligible subjects who had undergone successful spinal cord stimulation (SCS)-trial defined as ≥50% decrease in pain followed by SCS implant were collected and statistically analyzed. Patients were divided into four groups according to BMI. Self-reported pain scores on the 11-point numerical rating scale were collected at baseline, 6 months and 12 months post SCS-implant visits. Opioid utilization, if any, was collected at baseline and 12 months post-SCS implant. RESULTS: In all, 181 patients were included. Thirty-three were under and/or normal weight (≤24.9 kg/m2), 72 overweight (25.0-29.9 kg/m2), 63 obese (30.0-39.9 kg/m2), and 13 morbidly obese (≥40.0 kg/m2). The estimated coefficients from multivariable linear regression analysis were -1.91% (95% CI: -2.82% to -0.991%) and -1.48% (95% CI: -2.30% to -0.660%) reduction in pain improvement per unit increase of BMI for 6 months and 12 months scores, respectively. The estimated coefficient of disability status was -15.3% (95% CI: -22.1% to -8.48%). The estimated coefficient for 12 month opioid equivalence was -0.08% (95% CI: -0.14 to -0.021), per` 1 mg unit increase of morphine opioid equivalency. The data showed a statistically significant negative association between increasing BMI and SCS effectiveness at 6 and 12 months post-SCS therapy with a 2% reduction in efficacy for every unit increase of BMI after adjusting for confounding factors and a 20% better response in underweight and/or normal patients over the morbidly obese individuals which was not related to baseline pain score level. The significant difference in pain scores at 6 months (p = .0003) and 12 months (p = .04) post-SCS implant between obese and nonobese patients was not attributable to differences in baseline pain scores. There was no significant change in opioid utilization between baseline and 12 months post-SCS therapy. CONCLUSION: A negative association between SCS effectiveness and increasing BMI was found, whereas, no significant difference was noted amongst the various BMI cohorts and the daily opioid consumption.