Abstract
Objective Fatigue is common among people with inflammatory arthritis but is hard to manage. The aim of this study was to investigate how daily fluctuations in psychological variables correspond with changes in fatigue-related disability in the daily lives of people with inflammatory arthritis, and to identify factors to target in psychological interventions and routine clinical practice. Methods A cohort of 143 patients with rheumatoid arthritis (n = 97) or ankylosing spondylitis (n = 46) participated in a 10-day online diary study. Each evening participants completed a diary questionnaire assessing their fatigue, pain, fatigue-related disability, and 4 components of psychological flexibility (valued activity, mindfulness, cognitive fusion, and fatigue avoidance). Results On days when participants were more engaged in valued activities or more mindful, they reported less disability due to fatigue, even when controlling for levels of fatigue and pain that day. The daily psychological flexibility variables explained a total of 15.6% of the variance in daily fatigue-related disability. Conclusion Psychological flexibility variables are directly associated with fatigue-related disability in the daily lives of inflammatory arthritis patients. Further research is needed to investigate whether interventions that target psychological flexibility are effective at reducing fatigue-related disability.