Validation of the integral of pain relief as a measure of chronic pain treatment efficacy.

Introduction: Several scales are currently in use to measure chronic pain and its variations with treatments, as patient-reported outcomes; however, they are based only on pain intensity and neglect the duration of pain relief, critical to compare the efficacy of different treatments. Objectives: To assess the validity of the integral of pain relief (IPR), an index that combines the percentage and duration of pain relief, to compare the efficacy of various treatments. Methods: Patients undergoing intra-articular corticosteroid injections for knee osteoarthritis were recruited to validate the IPR. The pain intensity was assessed at baseline, using 2 different pain scales; and at follow-up visits 2, 4, 6, 8, and 12 weeks after the injection; adding the IPR and the patient's global impression of change (PGIC). The correspondence between the various scales and PGIC values was examined with data stratification, receiver operating characteristic curve analysis, and Spearman correlations. Results: In total, 66 patients were included in the analysis (20 men and 46 women, mean age 68.5 ± 9.2 years). All measures were strongly correlated, and the IPR could effectively identify responders at weeks 8 and 12, according to PGIC values, with a single value that can also be used for statistical analyses, unlike the PGIC. In addition, the IPR showed significant sex differences, with more effective and prolonged pain relief in women than in men ( Conclusion: The IPR demonstrated validity and responsiveness to assess the efficacy and duration of pain relief treatments in patients with chronic pain.