Depression in multiple sclerosis: relationship to planning ability.

Recent research has demonstrated deficits on effortful executive tasks involving planning in multiple sclerosis (MS) patients. Given the high prevalence of depression in MS and the commonly reported link between depression and performance on executive tasks, planning impairments in MS may be associated with depression. We compared the performance of depressed and nondepressed MS patients on a planning task (Tower of London-TOL) to evaluate this hypothesis. Compared with nondepressed MS patients, depressed MS patients made significantly (p < .05) more moves and took more time per trial on the TOL. A follow-up regression analysis was conducted that included the TOL and speeded attentional/working memory task indices found to be associated with depression in MS from the authors' prior reports. This analysis revealed that 25% of the variance in depression scores was predicted by the most sensitive speeded attentional/working memory task. Furthermore, this variance overlapped completely with variance predicted by the TOL-time/trial index. The only clearly nonspeeded task index, TOL-moves per trial, was associated with unique variance (8%) in predicting MS depression scores. These results suggest that slowed information processing speed and, secondarily, deficient nonspeeded central executive skill, may be core to the cognitive deficits characteristic of depressed MS patients.