Objectives: Fatigue is one of the most commonly reported symptoms in rheumatoid arthritis (RA). Many factors may play a causal role on fatigue in RA patients, but their contribution and interplay is barely understood. The objective was to develop a multidimensional model of factors that explain fatigue severity in RA.
Methods: A cross-sectional study (n=228) of consecutive patients with RA was performed. Fatigue, disease characteristics and psychosocial and behavioural outcomes were collected. Baseline differences between non severely fatigued patients (CIS-fatigue <35) and severely fatigued patients (CIS-fatigue ≥35) were tested. Structural equation modeling was used to test a hypothesised model for fatigue.
Results: The final model includes pain, physical functioning, mood, sense of control, sleep quality and fatigue, with good fit (CFI=0.976) explaining 74% of the variance in RA fatigue. Accordingly, poor sleep quality (β=0.42, p<0.001) and less physical functioning (β=0.65, p<0.001) are directly related to a higher level of fatigue. Less sense of control is related to more mood disturbance (β=0.64, p<0.001), more pain (β=0.389, p<0.001) and less physical functioning (β=-0.24, p<0.001). More mood disturbance is related to poor sleep quality (β=0.78, p<0.001) and higher pain level is related to less physical functioning (β=0.75, p<0.001).
Conclusions: RA fatigue is directly influenced by poor sleep quality and physical functioning, and indirectly by sense of control, mood and pain. Treatment of these factors by psychological interventions and physical exercise could help to improve fatigue in patients with RA.