ABSTRACT
BACKGROUND: There is evidence that subjective fatigue can influence cognitive functioning in multiple sclerosis (MS). DeLuca et al.'s (2004) Relative Consequence Model proposes that impairments to other high-level cognitive functions, such as memory, result from the disease's effect on information processing speed. OBJECTIVE: The primary aims of the study were to investigate both 1) the relationship between subjective fatigue and cognitive functioning, as measured by the widely used Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) in MS; and 2) the consequential effect of fatigue on information processing speed as predicted by the Relative Consequence Model. METHODS: 192 participants with MS attending tertiary referral MS centre completed the Modified Fatigue Impact Scale and BICAMS. RESULTS: Multiple correlation analyses determined that there were statistically significant relationships between all domains assessed by the BICAMS and levels of fatigue, such that higher levels of self-reported fatigue were associated with lower performance on information-processing, and visual and verbal learning. After controlling for information processing speed, the strength of correlation between fatigue and learning performance weakened. Linear regression analysis showed that fatigue predicted the most variance in verbal learning and 11.7% of the overall variance in BICAMS performance. CONCLUSION: Subjective fatigue and objective cognitive performance in MS are related. Caution is advised in the interpretation of BICAMS scores in cases where high levels of fatigue are present, and more detailed neuropsychological assessments may be required in order to accurately identify objective cognitive impairment independent of subjective fatigue.
