Interplay between patient global assessment, pain, and fatigue and influence of other clinical disease activity measures in patients with active rheumatoid arthritis

The interplay between patient-reported outcome measures in rheumatology is not well clarified. The objective of the study was to examine associations on the group level and concordance on the individual patient level between patient global assessment (PaGl), pain, and fatigue as scored on visual analog scales (VAS) in the daily clinic by patients with active rheumatoid arthritis (RA). Associations with other measures of disease activity were also examined. Traditional disease activity data on 221 RA patients with active disease planned to initiate biological treatment were extracted from the Danish DANBIO registry. Associations between VAS PaGl, pain, and fatigue (0-100) were examined using multiple regression analysis. Concordance between the VAS scores was expressed as the bias (mean difference between intra-individual scores) and the 95 % lower and upper limits of agreement (LLoA; ULoA) according to the Bland-Altman method. Mean age was 57 +/- 14 years, mean Disease Activity Score (DAS28-CRP4) 5.0 +/- 0.9, and mean PaGl 63.6 +/- 22.6. PaGl was most strongly predicted by pain and fatigue, pain by PaGl and fatigue, and fatigue by PaGl and pain (beta ranging from 0.17 to 0.69, p < 0.01-0.0001). More objective measures were not or far less predictive. LLoA;ULoA [bias] for PaGl vs. pain was -19.1; 29.5 [5.2], for PaGl vs. fatigue -22.8; 28.6 [2.9], and for fatigue vs. pain -29.2; 33.8 [2.3]. In conclusion, PaGl, pain, and fatigue were most strongly explained by each other, not by more objective clinical measures of disease activity and were nearly identical on the group level. On the individual patient level, however, differences between the scores varied considerably. The findings highlight the challenge of understanding and dealing with traditional patient-reported VAS measures when it comes to individual RA patients in the daily clinic.