Why do patients with chronic musculoskeletal pain reporting a clinically relevant change on disability not achieve such change in walking ability after interdisciplinary multimodal pain treatment?

PurposeInterdisciplinary multimodal pain treatment (IMPT) offers long-term benefits for patients with chronic musculoskeletal pain (CMP). Many patients, despite reporting a clinically relevant decrease of the self-reported Pain Disability Index (PDI), do not achieve such change for the 6-minutes walking test (6MWT). The objective is to identify factors that are associated with no clinically meaningful improvement on the 6MWT in patients with CMP who reported a clinically important improvement on disability (PDI) after 10-weeks of IMPT.Materials and methodsNine hundred and eighty-three patients reporting a clinically important change on the PDI (primary outcome) after IMPT were included. Logistic regression analysis was used to identify baseline and change scores of physiological and psychologic factors independently associated with a clinically important improvement on the 6MWT.ResultsThree hundred (32%) patients achieved a clinically important change on the 6MWT. A higher increase of the heart rate (HR) during the 6MWT at post-treatment compared to the HR increase at pre-treatment increases the probability of achieving a clinically relevant change on the 6MWT. Higher self-reported working capacity and anxiety at baseline resulted in a lower probability of achieving a clinically relevant increase of the metres walked.ConclusionsNone of the other factors targeted by IMPT contributed significantly to the final model. These results question the feasibility of the 6MWT as a secondary outcome measure as it merely seems to measure patient's behaviour (performance) and not capacity.