The effect of fatigue, sleep quality and depression on quality of life in patients with multiple sclerosis: A serial mediation model.

Background: Fatigue, depression and sleep problems are among the most common symptoms in patients with multiple sclerosis (PwMS) and are correlated with each other. In addition, these symptoms can have a significant impact on quality of life. The aim of this study was to investigate the impact of these symptoms on two different aspects of quality of life, physical and mental health, using a serial mediation model.

Method: This descriptive cross-sectional study was conducted with 178 PwMS between April and December 2019. Fatigue levels of the patients was assessed with the Fatigue Severity Scale (FSS), sleep quality with the Pittsburgh Sleep Quality Index (PSQI), depressive mood with the Beck Depression Inventory (BDI), and quality of life with the Multiple Sclerosis Quality of Life-54 Scale (MSQoL-54). A serial mediation analysis was performed to explore relationships between the parameters. Depressive symptoms were considered as predictors, sleep and fatigue as potential mediators and two dimensions of quality of life as outcome variables.

Results: The mean age of the 178 patients included in the study was 40.1 ± 11.0, and 66.3 % were female. Serial mediation analyses showed that higher depression scores were associated with poorer sleep quality (p < 0.01), and both increased depression and sleep problems were linked to greater fatigue (p < 0.01). The direct effect of depression, considered as a predictor in the model, on both sub-components of quality of life was negative and significant (p < 0.01). Additionally, depression was found to have an indirect effect on quality of life (both sub-component) in three different ways (p < 0.01). The first indirect effect was the through sleep. The second indirect effect was through fatigue. The third indirect effect was the effect of depression on quality of life through both sleep and fatigue. The direct and indirect effect of the depression variable explained the physical health sub-component of quality of life (QoL-PHC) at 71 % level. Also, the direct and indirect effect of the depression variable explained the mental health sub-component of quality of life (QoL-PHC) at 63 % level.

Conclusion: Depression was found to be an important predictor of quality of life (both sub-component) in PwMS. Sleep problems and fatigue were found to mediate the relationship between depression and physical and mental health quality of life. Management of these symptoms, which significantly impact the quality of life, is critical.