Fatigue, pain and patient global assessment responses to biological treatment are unpredictable, and poorly inter-connected in individual rheumatoid arthritis patients followed in the daily clinic

The objective of the study was to investigate relations on group level and agreements on the individual patient level between changes in fatigue, pain and patient global assessment (PaGl) assessed on visual analogue scales (VAS) in patients with rheumatoid arthritis (RA) after initiating or switching biological treatment. Associations with other disease measures were also examined. Traditional disease activity data on 177 patients with RA registered before and after 6-month treatment were extracted from the Danish DANBIO registry. Associations were examined using multiple regression analysis. Agreement between the VAS score changes (a dagger) was expressed as the bias (mean difference) and the 95 % lower and upper limits of agreement (LoA). All disease measures improved significantly. a dagger fatigue, a dagger pain and a dagger PaGl were independently associated with each other (r (partial) range 0.38-0.81, p < 0.0001), but not to a significant degree with changes in other measures. Lower and upper LoA [bias] for a dagger fatigue versus a dagger pain was -44.0 and 51.8 [3.9], for a dagger fatigue versus a dagger PaGl -38.2 and 52.4 [4.2], and for a dagger PaGl versus a dagger pain -34.3 and 34.3 [0.0]. a dagger fatigue, a dagger pain and a dagger PaGl were independently but weakly predicted by their own baseline values (r (partial) range -0.30 to -0.46, p < 0.0001). In conclusion, changes in fatigue, pain and PaGl were independently associated and nearly identical on group level but agreements were poor in individual patients. The changes were poorly explained by other potential predictor variables and by baseline values. The results expose the unpredictable nature of patient-reported VAS scores in individual patients with RA.