Longitudinal consistency of the relationship between depression symptoms and cognitive functioning in multiple sclerosis

Background: Lifetime prevalence rates of cognitive dysfunction and depression in multiple sclerosis (MS) have typically been reported to be similar to 50%. However, an inconsistent relationship between these two common features of MS has been reported in the literature. Because neurovegetative depression symptoms overlap with MS symptoms, it may be that literature inconsistencies can partly be explained by the fact that only those depression symptom clusters unambiguously reflective of depression are associated with cognitive dysfunction. Objective: To explore the relationship between different depression symptom clusters and a battery of tests measuring cognitive domains commonly impaired in MS and was examined at two time points 3 years apart. Methods: The Chicago Multiscale Depression Inventory was employed to measure mood, negative evaluative, and neurovegetative symptom clusters in 53 MS patients who were also administered a battery of neuropsychological tests. Results: At time point 1, Mood and Evaluative Chicago Multiscale Depression Inventory scales were significantly associated with tasks of complex speeded attention, planning, and working memory. At time point 2, the Evaluative scale was still significantly associated with these domains, in addition to spatial memory; however, all of the significant correlations with the Mood scale dropped out. Conclusion: These results show that negative evaluative depression symptoms are most consistently predictive of cognitive dysfunction in MS. It may be that negative evaluative depression symptoms use up available cognitive capacity, thus compromising performance on cognitive capacity demanding tasks in MS patients.