Depression influences fatigue in inflammatory bowel disease amongst other factors: a structural modelling approach.

Objectives: Fatigue is common in people with inflammatory bowel disease (IBD) and is associated with IBD activity, sleep disturbance, anxiety and depression. The relative contribution of these factors to fatigue is unclear. This study aimed to investigate the relationship between fatigue and these factors through a novel approach using structural equation modelling.

Design: Online questionnaire circulated via three tertiary IBD centres and Crohn's Colitis Australia.

Methods: Fatigue was assessed using the Functional assessment of chronic illness measurement system fatigue subscale. Validated measures of sleep, anxiety, depression and IBD activity were included. Following correlation analyses, a structural equation model was developed for the outcome of the fatigue score. Direct and indirect effects were calculated.

Results: There were 630 complete responses to the online questionnaire. The median age of respondents was 41 with the majority female and over half (52%) on biologic medication. Structural equation models for Crohn's disease and ulcerative colitis demonstrated a good fit. In Crohn's disease, the relationship between IBD activity and fatigue was mostly mediated indirectly through the influence of IBD activity on sleep, anxiety and primarily depression. Sleep quality mediated the influence of IBD activity and the indirect effects of depression on fatigue, but not anxiety. Unlike in Crohn's disease, the direct influence of IBD activity on fatigue in ulcerative colitis was non-negligible, although remained of lesser magnitude than the indirect effect of IBD activity on fatigue. Depression was the primary indirect mediator of the influence of IBD activity on fatigue in ulcerative colitis.

Conclusion: In Crohn's disease, IBD activity leads to fatigue through its influence on sleep quality and mental health. The data suggest treatment of clinically significant depression, in both ulcerative colitis and Crohn's disease, may result in the largest decline in fatigue score compared to other variables. Treatment algorithms for fatigue should consider depression a priority.