Cognitive fatigue in multiple sclerosis: Do self-reports of fatigue correspond with actual reductions in cognitive performance over a single testing session?

Background and aims: Individuals with multiple sclerosis (MS) differentiate their experience of cognitive from physical fatigue. However, the concept of cognitive fatigue and how it is appraised is poorly understood. This study examines the relationship between self-reported fatigue and actual change in cognitive performance over a single testing session to further our understanding of MS-related cognitive fatigue.

Method: Thirty-one participants with MS and 30 matched healthy control participants completed the Modified Fatigue Impact Scale (mFIS) and were assessed twice on the Brief Repeatable Neuropsychological Battery (BRNB) and Conners Continuous Performance test (CPT) over a 2.5 hour testing session. A visual analogue scale for fatigue (VAS-F) was administered at baseline, and immediately following the first and second CPT administration.

Results: MS participants performed more poorly than healthy participants on most psychological tests, and performance over the session changed in a manner consistent with healthy controls on BRNB tasks. Whereas CPT performance declined over time in the MS participants, it improved in healthy participants. The MFIS had small-to moderate correlations with Conners performance. Further, whereas high correlations were detected between change in VAS-F scores and change in Conners index scores for the healthy control participants, there was negligible correlations for individuals with MS.

Conclusions: The results provide support for a temporal fatigue hypothesis in explaining MS-related fatigue. Individuals with MS also appear less able to accurately appraise changes in cognitive functioning, indicating that factors other than changes in levels of cognitive functioning are related to the experience of cognitive fatigue in MS.