Objectives: This pilot study examined sensitivity to change and relative independence of fatigue as an outcome measure in patients with psoriatic arthritis (PsA) following anti-TNF therapy.
Methods: Patients with PsA commencing anti-TNF therapy were evaluated at baseline and at 3 months. Fatigue was measured using a 0-10 numeric rating scale (NRS). This was a one-dimensional 11-point NRS with anchors of 0 (none) and 10 (a great deal). The words 'none' and 'a great deal' were placed under the NRS corresponding to the anchors 0 and 10, respectively. Sensitivity to change of fatigue was compared with recognised core outcomes and determined by calculating the standardised response means. Multiple regression analysis was employed to determine predictors of fatigue and their independent variance.
Results: Forty-one patients were evaluated. Mean (SD) fatigue levels were 5.6 (2.3) and 3.6 (2.2) (p=0.001) at baseline and at 3-months, respectively. Using the SRM, fatigue ranked sixth relative to the other measures demonstrating a moderate sensitivity to change. Noteworthy was the observation that fatigue was ranked higher than CRP. The relative independent variance in fatigue of 27% was greater than that of the core clinical measures: HAQ 21%, TJC 14%, Pain 4%, SJC 0.4%, GH 0.4%, and less than that of the laboratory measure CRP 33%.
Conclusions: This study demonstrated that fatigue is an independent outcome measure and is sensitive to change in patients with PsA.