Responsiveness and minimal important change of the Pain Catastrophizing Scale in people with chronic low back pain undergoing multidisciplinary rehabilitation.

Background The Pain Catastrophizing Scale (PCS), a widely used tool to assess catastrophizing related to spinal disorders, shows valid psychometric properties in general but the minimal important change (MIC) is still not determined. Design Prospective observational study. Aim To assess responsiveness and MIC of the PCS in individuals with chronic low back pain (LBP) undergoing multidisciplinary rehabilitation. Setting Outpatient rehabilitation hospital. Population Two hundred and five patients with chronic LBP. Methods Before and after an 8-week multidisciplinary rehabilitation program, 205 patients completed the Italian version of the PCS (PCS-I). We calculated the PCS-I responsiveness by distribution-based methods [effect size, ES; standardised response mean, SRM; minimum detectable change, MDC] and anchor-based methods [receiver operating characteristic (ROC) curves]. After the program, participants completed a 7-point global perceived effect scale (GPE), based on which they were classified as "improved" vs. "stable". ROC curves computed the best cut-off level (taken as the MIC) between the two groups. ROC analysis was also performed on subgroups according to patients' baseline PCS scores. Result ES, SRM and MDC were 0.71, 0.67 and 7.73, respectively. ROC analysis yielded an MIC of 8 points (95% confidence interval [CI]: 6-10; area under the curve [AUC]: 0.88). ROC analysis of the PCS subgroups confirmed an MIC of 8 points (95%CI: 6-10) for no/low catastrophizers (score 30, n=33; AUC: 0.84). Conclusions The PCS-I showed good ability to detect patient-perceived clinical changes in chronic LBP post-rehabilitation. The MIC values we determined provide a benchmark for assessing individual improvement in this clinical context. Clinical rehabilitation impact The present study calculated - in a sample of people with chronic LBP - the responsiveness and MIC of the PCS. These values increase confidence in interpreting score changes, enhancing their meaningfulness for both research and clinical contexts.