The association between pain intensity and disability in patients with failed back surgery syndrome, treated with spinal cord stimulation

Objective: Pain researchers demonstrated that pain intensity is not the most reliable measure of the success of chronic-pain treatment. Several research groups have proposed "core outcome domains", such as measurements of disability, to assess the effect of an intervention in pain patients. Up till now, studies investigating the relation between pain intensity and disability in patients treated with spinal cord stimulation (SCS) are lacking. Therefore, the current objective is to examine which pain-reporting strategy, routinely used in pain research, associates best with the degree of disability in these patients. Methods: Eighty-one failed back surgery syndrome patients (37 males and 44 females, mean age 54.6 years), treated with high-dose spinal cord stimulation (HD-SCS) are recruited. Pain intensity was scored on an 11-point numerical rating scale (NRS) for leg and back pain, while disability was assessed with the Oswestry disability index (ODI). The association between both variables was investigated with Spearman's correlation and Cramer's V. Results: Significant correlations (p < 0.001) are found between the absolute and relative differences of the ODI and NRS. Significant associations were found between reported cut-offs in literature (<= 3, <= 5, and 50% pain relief) and the degree of disability. Finally, a significant association (p < 0.001) was found between the minimal clinical important difference. Conclusions: In this study, we showed that the degree of disability was strongly associated with the pain intensity as measured using different methods. The standard method for reporting pain intensity reduction (50%) seems to associate the strongest with the degree of disability. However, a low degree of disability does not always reflect a low pain intensity.