Do patient-reported measures of disease activity in rheumatoid arthritis vary between countries? Results from a Nordic collaboration.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked DownloadObjectives: To investigate whether patient-reported outcomes vary across countries and are influenced by cultural/contextual factors. Specifically, we aimed to assess inter-country differences in tender joint count (TJC), pain and patient's global health assessment (PGA), and their impact on disease activity (DAS28-CRP) in rheumatoid arthritis (RA) patients from five Nordic countries. Methods: We collected data (baseline, 3- and 12-months) from rheumatology registers in the five countries comprising RA patients starting a first-ever methotrexate or a first-ever tumor necrosis factor inhibitor (TNFi). In order to assess the role of context (=country), we separately modelled TJC, pain and PGA as functions of objective variables (C-reactive protein, swollen joint count, age, sex, calendar period and disease duration) with linear models. Analyses were performed at each time point and for both treatments. We further assessed the impact of inter-country differences on DAS28-CRP. Results: 27 645 RA patients started methotrexate and 19 733 started a TNFi. Crude inter-country differences at methotrexate start amounted to up to 4 points (28 points scale) for TJC, 10 and 27 points (0-100 scale) for pain and PGA, respectively. Corresponding numbers at TNFi start were 3 (TJC), 27 (pain) and 24 (PGA) points. All differences were reduced at 3- and 12-months, and attenuated when adjusting for the objective variables. The variation in predicted DAS28-CRP across countries amounted to < 0.5 units. Conclusions: Inter-country differences in TJC, pain and PGA are greater than expected based on differences in objective measures, but have a small clinical impact on DAS28-CRP across countries. Keywords: Patient-reported outcome (PRO); disease activity; inter-country comparison; pain; rheumatoid arthritis