The mediating role of processing speed in the relationship between depressive symptoms and cognitive function in multiple sclerosis

Introduction: Although disorders of mood and cognition are frequently observed in multiple sclerosis, their relationship remains unclear. We aimed to investigate whether this mood-cognition relationship is mediated by inefficient processing speed, a deficit typically associated with mood symptomatology in the psychiatric literature and a common deficit observed in multiple sclerosis patients. Method: In this study, comprehensive cognitive data and self-reported mood data were retrospectively analyzed from 349 patients with relapsing remitting multiple sclerosis. We performed a bootstrapping analysis to examine whether processing speed provided an indirect means by which depressive symptoms influenced cognitive functioning, specifically memory and executive function. Results: We observed that processing speed mediated the relationship between depressive symptoms and measures of memory and executive function. Interestingly, exploratory analyses revealed that this mediational role of processing speed was specific to MS patients who were younger, had a lower disability level, and had fewer years since MS diagnosis. Conclusions: Together, these findings have implications for mood and cognitive intervention with multiple sclerosis patients.