Fatigue is the worst debilitating symptom of patients with MS (multiple sclerosis) as it severely limits their participation in the public sphere and the workforce, besides alienating their interpersonal relationships. It has a subjective component, i.e. how patients feel, and an objective one, i.e. the diminished performance in physical and intellectual tasks. Kluger et al. created a unified taxonomy to guide its treatment in the medical settings.
Perceived fatigue is what the patient actually feels at any given time; it can be defined as a lack of purpose in daily activities that hampers performance.
Fatigability (also called performance fatigability) is what can be objectively measured by an examiner; it is defined by the measure of change in the performance of a physical or a cognitive task over a certain period of time.
Perceived fatigue is measured by the “Neurological Fatigue Index” (NFI-MS), which was approved by the FDA. It is made of 23 standard questions that cover three domains of fatigue; physical, cognitive and sleep quality. It also has a summary scale that covers the physical and cognitive domains. Fatigability can be measured with a 6-Minute Walk Test (6MWT), a grip strength test and the response speed to different cognitive tests. The third measurement of fatigability is carried out with the “Continuous Performance Test” (CPT) that checks the timely attention in front of a computer screen.
Mayis Aldughmi et al. studied the perceived fatigability and fatigability in 52 patients with mild forms of MS with a mean age of 46 years. The percent change score of the 6MWT was not statistically associated with the physical domain, the cognitive domain or the summary scale. The grip strength test change scores were not statistically associated with physical domain, the cognitive domain or the summary scale. But the performance fatigability was statistically associated with the three parameters of the NFI-MS. The data illustrates that performance fatigability during an attention-based test is associated with increased physical and cognitive perceived fatigue and the overall perceived fatigue. However those assessments of performance fatigability during a physical task did not yield some significant results. This study showed that the presence of depression was associated with fatigue.
In this study MS patients had fatigue after 3 performance fatigability tests: walking, handgrip and attention. Only attention had a statistically significant association with perceived fatigue, unlike the other 2 performance measures.
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