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 (∆) was expressed as the bias (mean difference) and the 95 % lower and upper limits of agreement (LoA). All disease measures improved significantly. ∆fatigue, ∆pain and ∆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 ∆fatigue versus ∆pain was -44.0 and 51.8 [3.9], for ∆fatigue versus ∆PaGl -38.2 and 52.4 [4.2], and for ∆PaGl versus ∆pain -34.3 and 34.3 [0.0]. ∆fatigue, ∆pain and ∆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.