Multiple Sclerosis Patient Fatigue Depends on Task Length

Fatigue exhibited by multiple sclerosis (MS) patients is related to the task they are involved in, according to findings published in Frontiers in Neurology.

Researchers from the Kessler Foundation compared 32 MS patients and 24 healthy controls who completed experimental tasks in order to investigate the relationship between subjective and objective cognitive fatigue, information processing domain, cognitive load, and time on task in patients with MS. Participants completed tasks and were measured for processing speed (PS) and working memory (WM) using an analog scale at baseline and at multiple time points through the duration of the experiment. All of the patients in the study were right handed, and were at least 1 month from their last exacerbation (for only MS patients). Over a 2 week period, patients were evaluated over 2 separate sessions.

The participants completed WM tasks using building blocks and were instructed to respond when certain letters appeared. Fatigue levels were measured throughout the different tasks. At the same time, participants were asked about their feelings of fatigue at specific points of time when asked by the researchers, and they were instructed to ignore that fatigue up to that point of being asked.

The MS patient group demonstrated high fatigue than the control group across sample tasks. But, the researchers noted, there was no association between any of the other independent variables in the MS patient group.

“Task length was the factor associated with subjective cognitive fatigue which supports the hypothesis of Temporal Fatigue,” explained lead author Joshua Sandy, PhD, in a press release. “This finding should be considered when designing cognitive studies in MS populations. More research is needed to look at these parameters in people with different types of MS, different levels of cognitive impairment and in more advanced stages.”

The researchers wrote they believed that researchers should consider sustained task length when investigating cognitive fatigue and that further research is needed to confirm the hypothesis.

“The present findings suggest that MS participants experience subjective cognitive fatigue as the time of the task increased, regardless of the cognitive domain, and regardless of the cognitive load associated with the task,” the authors concluded. “Additionally, the MS group may have had to work harder than the HC group to achieve equivalent performance, and this extra effort resulted in higher fatigue. It remains possible that cognitive fatigue increased as a result of cognitive load or cognitive domain; however, this may have resulted in participants exerting more effort to maintain efficient performance.”