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Lower ratings of pain intensity in older adults lead to underestimation of disease activity in patients with rheumatoid arthritis

Yong Gil Hwang, Ajay D Wasan, June Feng, Heather Eng, Jason Lyons, Anthony Fabio & Larry W Moreland

Background: To investigate the influence of age on the components of the 28-joint Disease Activity Score (DAS28)-C-Reactive Protein (CRP) in patients with Rheumatoid Arthritis (RA) and whether DAS28-CRP can be equally interpreted in all age groups. Methods: The proportion of CRP and patient reported components of the DAS28 (DAS-P) were analyzed and compared between 2 age groups (younger RA <60, older RA ≥ 60) using Mann-Whitney U test. Inflammatory disease burden in the joint was calculated by modified DAS28 (MDAS28=0.49 x ln(C-Reactive Protein (CRP))+0.15 x swollen joint count 28+0.22 x physician global assessment (PhGA)+1). Multivariate analyses were used to design models best predicting the effect of age on CRP, the proportion of CRP, inflammation level calculated by MDAS28, DAS-P, and pain levels. Results: CRP and the proportion of CRP in DAS28-CRP were not influenced by age. MDAS28 did not increase with age but was associated with disease duration and anti-tumor necrosis factor (TNF) therapy. DAS-P and pain level had significant negative association with age. In subjects with moderate inflammation (defined by MDAS28 score above 50 percentile, N=370), older RA subjects (N=189) had lower pain level, tender joint count, patient and physician global assessment, DAS28-CRP than younger subjects (n=157). Conclusions: CRP, proportion of CRP in DAS28-CRP, and MDAS28 were not influenced by age but the proportion of subjective components of DAS28-CRP and pain level decreased with age. Therefore, disease activity could be underestimated by DAS28-CRP in older RA patients.