The minimal important change (MIC) for the pain disability index (PDI) in individuals with chronic musculoskeletal pain

Chronic musculoskeletal pain (CMP) is a prevalent health issue, causing significant limitations in daily functioning. The Pain Disability Index (PDI) is commonly used to measure pain-related disabilities, but its minimal important change (MIC) is understudied in CMP. Therefore, the aim of the current study was to evaluate the MIC of the PDI in individuals with CMP undergoing an interdisciplinary multimodal pain treatment (IMPT) program. A prospective cohort study including individuals who completed a 10-week IMPT program between 2019 and 2024 across rehabilitation clinics in The Netherlands was conducted. The PDI and the Global Perceived Effect (GPE) were used to assess disability and patients' recovery perspective. The MIC was determined using anchor-based predictive modeling, with the GPE as the external anchor. Among the 3656 individuals with CMP included in the analysis, 84.2% reported important improvement and 3.5% reported important deterioration. The MIC for improvement was 6.05 points and 9.27 points for deterioration. The measurement error of the PDI was 16.53 points. The PDI is insufficiently sensitive for assessing clinically meaningful changes in individual patients due to its high measurement error. Alternative measures, such as patient-specific questionnaires or the GPE, are recommended for individual monitoring in clinical practice.