Clinical important improvement of chronic pain patients in randomized controlled trials and the DATAPAIN cohort.

BACKGROUND

Change on the Numeric Rating Scale (NRS) is based on subjective pain experience, hampering the establishment of clinically important improvement. An anchor-based method, the Patients' Global Impression of Change (PGIC), is often added to determine whether a patient has improved. A two-point change on the NRS has been shown to be equivalent to a moderate clinically important improvement in randomized controlled trials (RCT's) on medication effects. We contemplated whether these findings could be reproduced in cohort and data and in non-drug interventional RCT's.

METHODS

The NRS change was quantified by subtracting the NRS of baseline from the NRS at 6-month follow-up. Categorization of success/nonsuccess was applied on the PGIC, and their average NRS raw changes were calculated. The Spearman correlation coefficient quantified the overall relationship, while the discriminative ability was explored through the receiver operating characteristic curve. Data were stratified on design, sex, and pain intensity at baseline. Besides, the cohort evaluated treatment status at follow-up.

RESULTS

The records of 1661 patients were examined. Overall, the observed NRS change needed for moderate clinically important improvement was larger than the average two points. Yet, the changes in the cohort were smaller compared with the RCT's. Moreover, it modified with pain intensity at baseline and treatment statuses indicated differences in mean clinical importance of -4.15 (2.70) when finalized at 6 months and -2.16 (2.48) when treatment was ongoing.

CONCLUSION

The moderate clinically important improvement varied substantially, representing heterogeneity in pain relief and its relation to treatment success in chronic pain patients.