Osteoarthritis patients with pain improvement are highly likely to also have improved quality of life and functioning. A post hoc analysis of a clinical trial
Authors: Peloso Paul M. , Moore R. Andrew , Chen Wen-Jer , Lin Hsiao-Yi , Gates Davis F. , Straus Walter L. , Popmihajlov Zoran 
Published: August 2016

Abstract

Background
This analysis evaluated whether osteoarthritis patients achieving the greatest pain control and lowest pain states also have the greatest improvement in functioning and quality of life.

Methods
Patients (n = 419) who failed prior therapies and who were switched to etoricoxib 60 mg were categorized as pain responders or non-responders at 4 weeks based on responder definitions established by the Initiative on Methods, Measurement, and Pain (IMMPACT) criteria, including changes from baseline of ≥15%, ≥30%, ≥50%, ≥70% and a final pain status of ≤3/10 (no worse than mild pain). Pain was assessed at baseline and 4 weeks using 4 questions from the Brief Pain Inventory (BPI) (worst pain, least pain, average pain, and pain right now), and also using the Western Ontario and McMaster Universities Arthritis Index (WOMAC) pain subscale. We examined the relationship between pain responses with changes from baseline in two functional measures (the BPI Pain Interference questions and the WOMAC Function Subscale) as well as changes from baseline in quality of life (assessed on the SF-36 Physical and Mental Component Summaries). We also sought to understand whether these relationships were influenced by the choice of the pain instrument used to assess response. We contrast the mean difference in improvements in the functional and quality of life instruments based on pain responder status (responder versus non-responder) and the associated 95% confidence limits around this difference.

Results
Patients with better pain responses were much more likely to have improved functional responses and improved quality of life, with higher mean changes in these outcomes versus pain nonresponders, regardless of the choice of IMMPACT pain response definition (e.g., using any of 15%, 30%, 50%, 70% change from baseline) or the final pain state of ≤3/10. There was an evident gradient, where higher levels of pain response were associated with greater mean improvements in function and quality of life. The finding that greater pain responses led to greater functional improvements and quality of life gains was not dependent on the manner in which pain was evaluated. Five different pain instruments (e.g., the 4 questions on pain from the BPI pain questionnaire and the WOMAC pain subscale) consistently demonstrated that pain responders had statistically significantly greater improvements in function and quality of life compared to pain non-responders. This suggests these results are likely to be generalizable to any validated pain measure for osteoarthritis.

Conclusions
Pain is an efficient outcome measure for predicting broader patient response in osteoarthritis. Patients who do not achieve timely, acceptable pain states over 4 weeks were less likely to experience functional or quality of life improvements.

Implications
Good pain improvements in osteoarthritis with a valid pain instrument are a proxy for good improvements in both function and quality of life. Therefore proper osteoarthritis pain assessment can lead to efficient evaluations in the clinic.