A 3-year longitudinal study of cognitive impairment in patients with primary progressive multiple sclerosis: speed matters.

Background: The few controlled longitudinal studies of cognitive performance in MS patients all provide evidence of deterioration in at least a subset of the patients sampled. Only one of these studies has focused on primary progressive MS, and little attention has been paid to the specific domains of cognitive functioning that change over time. The present study examined three principal cognitive domains in samples of primary progressive MS patients and healthy controls followed over a period of 3 years.

Methods: A battery of neuropsychological tests that included measures of strategic problem solving, verbal memory, and information processing speed was administered annually to 24 MS patients and 25 controls.

Results: MS patients' performance on measures of processing speed showed significantly greater decline over the 3-year period than did that of controls. Similar results were not observed in the case of problem solving or verbal memory. There was no evidence of more dramatic decline occurring in patients who were initially classified as cognitively impaired relative to those who were unimpaired at baseline. However, this failure may have been influenced by differential attrition from the sample; more impaired patients were less likely to complete the study.

Conclusion: Overall the results support the contention that information processing speed is the domain most sensitive to the impact of multiple sclerosis on cognitive functioning over time.