Association Between Levels of Functional Disability and Health-Related Quality of Life With Spinal Cord Stimulation for Chronic Pain

Objectives: Pain score, functional disability, and health-related quality of life (HRQoL) are core outcome domains for chronic pain clinical trials. Although greater levels of pain reduction have been shown to be linked to larger gains in HRQoL, little is known of the association between HRQoL and disability in the setting of chronic pain. The aims of this study were to 1) investigate the association between functional disability and HRQoL and 2) estimate the utility values associated with levels of functional disability in patients treated with evoked compound action potential (ECAP) spinal cord stimulation (SCS) for chronic pain.

Materials and methods: Data on functional disability assessed using the Oswestry Disability Index (ODI) and HRQoL (EQ-5D-5L) were collected from 204 patients with an Evoke ECAP-SCS device and followed up to 12 months. SF-6D utility scores also were retrieved for 134 of these patients. Multivariable linear regression models adjusted for baseline utility values and patient demographics were used to compare differences in utility values across ODI categories.

Results: Significant improvements in functional disability and HRQoL were observed at three- and 12-month follow-up after SCS. Patients reporting "minimum disability," "moderate disability," "severe disability," and "crippled" had mean EQ-5D scores of 0.82, 0.73, 0.59, and 0.45, respectively. The mean change in EQ-5D score was 0.007 per unit change in total ODI score. The R² statistic showed a moderate level association (49%-64% of variance in EQ-5D explained by ODI).

Conclusion: ECAP-SCS results in significant improvements in functional disability and HRQoL. This study shows that improvement in function of people with chronic pain before and after ECAP-SCS is associated with improvement in HRQoL.