(PS1-90) Examining the Temporal Dynamics and Correlates of Fatigue in Depression

Abstract Text: Fatigue is a prevalent and debilitating symptom of Major Depressive Disorder (MDD). Yet, despite its clinical significance, the nature of fatigue in MDD remains poorly understood. One barrier is reliance on retrospective self-reports, which provides minimal insight into temporal dynamics or within-person inter-symptom relationships. In this study, we utilize ecological momentary assessment (EMA) to examine temporal dynamics of fatigue and its intra- and inter-individual associations with other core symptoms of depression.

Participants were adults with MDD during a current major depressive episode (N = 69) and a healthy control group who did not meet criteria for any history of psychiatric illness (N = 90). Participants were predominately White (73%), not Hispanic or Latino (89%), and female (76%). MDD was assessed via the Mini-International Neuropsychiatric Interview and Beck Depression Inventory-II (BDI-II). EMA surveys were delivered 5x per day for 3 weeks at 3-hour intervals. At each prompt, participants reported fatigue ("I have a lack of energy"), depressed mood (“I feel depressed or down”), and anhedonia (“I have little interest or pleasure in doing things”) on a scale from 0 (Not at all) to 100 (Very much).

Relative to health controls, participants with MDD experienced fatigue with greater intra-individual frequency, intensity, standard deviation (SD), and root mean square of successive differences (RMSSD), ts ≥ |-5.86|, ps <.001. In multilevel models, we observed quadratic effects of time such that fatigue initially decreased (b = -3.25, p < .001) before increasing in the afternoon/evening (b = 6.89, p < .001). The initial decrease was more pronounced in the MDD group (p = .046). In multilevel dynamic structural equation models (DSEM), we observed reciprocal dynamic relationships between depressed mood and fatigue. Depressed mood was associated with increased fatigue at the same time point (β = 0.19 [0.17-0.21]) and approximately 3 hours later (β = 0.05 [0.03-0.08]). Individuals also tended to report greater depressed mood following increased fatigue (β = 0.07 [0.05-0.09]). The same-moment covariance between fatigue and depressed mood was higher among individuals with greater depressive symptoms (β = 0.22 [0.08-0.34]). A comparable pattern of findings was observed for the relationship between fatigue and anhedonia. Moreover, fatigue was more strongly associated with next-prompt anhedonia among individuals with greater depressive symptoms (β = 0.62 [0.38-0.76]).

Relative to healthy control participants, individuals with MDD reported more frequent, intense, and variable fatigue, and were also distinguished by elevated fatigue in the morning. The strong reciprocal relationships among fatigue, depression, and anhedonia, and the finding that those relationships were stronger in those with major depression suggest that fatigue may not merely be a passive consequence of depression but rather an active contributor to symptom maintenance. Future research should investigate the mechanisms driving these temporal relationships and develop more precise, real-time assessments of fatigue to inform targeted interventions that address fatigue and improve MDD outcomes.