The impact of subjective cognitive fatigue and depression on cognitive function in patients with multiple sclerosis

Abstract

Background: The association between subjective cognitive fatigue and objective cognitive dysfunction in patients with multiple sclerosis (PwMS) has been studied, with conflicting results. Objective: To explore the impact of fatigue on cognitive function, while controlling for the influence of depression, disability, comorbidities, and psychotropic medications. Methods: PwMS completed a computerized cognitive testing battery with age- and education-adjusted cognitive domain scores. Disability (Expanded Disability Status Scale (EDSS)), cognitive fatigue, and depression were concurrently evaluated. Results: In all, 699 PwMS were included. Both cognitive fatigue and depression were significantly and negatively correlated with the same cognitive domains: information processing speed, executive function, attention, motor function, and memory (−0.15 ⩽ r ⩽ −0.14 for cognitive fatigue; −0.24 ⩽ r ⩽ −0.19 for depression). Multivariate analysis revealed significant but small independent correlations only between depression and neuropsychological test results, while cognitive fatigue had no independent correlation with objective cognitive function except for a trend toward impaired motor function in highly fatigued PwMS. Depression and cognitive fatigue accounted for no more than 6% of the variance in objective cognitive domain scores. Conclusion: Cognitive fatigue is not independently related to objective cognitive impairment. Depression may influence cognitive function of PwMS primarily when it is severe. Cognitive impairment in PwMS should not be ascribed to fatigue or mild depression.