Fatigue and declines in cognitive functioning in multiple sclerosis

Objective: To determine whether cognitive fatigue, defined as a decline in cognitive performance over a single testing session, could be identified in MS. Methods: Forty-five individuals with MS and 14 healthy control partici pants completed a 4-hour session of cognitive testing that involved a basel ine neuropsychological battery, a continuous effortful cognitive task (comp leting mental arithmetic problems administered on a computer), and a repeat neuropsychological battery. Self-report measures of fatigue and affect wer e completed before each step of the testing session. Results: The pattern o f change in cognitive performances over the testing session significantly d iffered between the MS and control participants. Individuals with MS showed declines on measures of verbal memory and conceptual planning, whereas the control participants showed improvement. Although there were no significan t differences between the groups on any of the baseline cognitive measures, the MS participants performed worse than the control subjects on tests of visual memory, verbal memory, and verbal fluency that were repeated followi ng the continuous effortful cognitive task. Both MS and control participant s reported increased mental and physical fatigue across the testing session compared with their baseline values. Conclusion: Individuals with MS show declines in cognitive performance during a single testing session and fail to show the improvement exemplified by healthy control subjects.