By Annette M. Boyle
Multiple sclerosis patients often report fatigue, but it isn’t always clear how that condition affects their functionality. New research is seeking to establish clearer definitions and measures of fatigue in an effort to help improve quality of life for MS patients.
WASHINGTON—Of all the symptoms of multiple sclerosis, fatigue consistently rates as the most debilitating and most common. How the neurodegenerative disease causes fatigue and how it can best be measured and ameliorated remains unclear, but two VA researchers suggest that clearly separating the perception of fatigue from fatigability can move research forward.
The researchers, Bryant Seamon, DPT, a clinical research associate in the Muscle Morphology, Mechanics and Performance Laboratory (MMMPL) and Michael Harris-Love, DSc, MPT, director of the MMMPL at the Washington, DC, VAMC outlined the limitations of current fatigue assessments in multiple sclerosis (MS) in a recent article in Frontiers in Neurology.1
“We have all experienced fatigue (often expressed as a feeling of tiredness or exhaustion), it is becoming more apparent that there is not always a direct link between how ‘fatigued we feel’ and how long we can perform a given task. This is supported by studies that show how fatigue questionnaires do not consistently correlate with activity performance,” Harris-Love explained.
They noted that exercise interventions often show significant changes in functional capacity and independence measures, but patients report only slight changes in fatigue scores on questionnaires. Conversely, self-reported fatigue has a stronger correlation to depression than to current clinical measures for fatigue symptoms in MS, isometric measures of muscle fatigue or functional assessments such as gait speed or the six-minute walk test.
To increase the utility of fatigue measures, Seamon and Harris-Love advocated dividing fatigue into two trait components that can be evaluated separately: the perception of fatigue and the ability to perform a task. “’Perception of fatigue’ defines subjective sensations related to an individual’s symptom complaint and is the result of homeostatic and psychological factors. ‘Fatigability’ relates to task performance and is defined by a change in performance relative to an objective criterion,” they wrote.
“There is a glaring research gap in understanding how these traits of fatigue impact someone’s daily living, which is important to both neurologists and rehabilitation professionals.” Seamon told U.S. Medicine. “If fatigue is a multiple trait symptom, then treatment should be aimed at addressing those traits specifically. Unfortunately, we face a difficult challenge to target specific traits without ways of specifically assessing them.”
Measuring anaerobic fatigue and muscle performance provides more useful information and better correlates with ability to perform activities of daily living, which are typically relatively short tasks that involve less than maximum muscle force, Harris-Love said. Further, “anaerobic performance can tell us a great deal about muscle physiology and neuromuscular performance, which can be impaired in individuals with MS,” he added. That information can help rehabilitation professionals treat the underlying mechanisms that contribute to fatigue.
The researchers recommend obtaining objective measures of muscle performance, including muscle force and muscle fatigue, as well as an assessment of function when doing an evaluation for an MS patient. They also noted that various tests used to evaluate function, such as the sit-to-stand test and the 25-foot walk, measure quite different performance parameters. Tests that more closely parallel requirements of daily living—notably, the Short Physical Performance Battery Protocol, Adult Myopathy Assessment Tool and the Functional Capacity Test—may provide better clinical assessments and indications of intervention effectiveness, particularly if their scores can be related to performance on fatigue tests in aerobic and anaerobic conditions.
Adopting quantifiable clinical measures of performance fatigability would enable researchers and rehabilitation professionals to use the response to interventions as the basis for recommendations for specific exercises. Together these steps could help clinicians guide patients “toward the goals of “minimizing debilitating fatigue, improving functional performance, and enhancing their quality of life,” Harris-Love and Seamon noted.
Still, because of the differences in individual’s perception of fatigue and their actual performance, the researchers recommended that rehabilitation professionals use both a questionnaire that measures perceptions and an objective, task-based measure of functional ability to evaluate a patient’s response to a treatment plan.
- Seamon BA, Harris-Love MO. Clinical Assessment of Fatigability in Multiple Sclerosis: A Shift from Perception to Performance. Front Neurol. 2016 Nov 7;7:194. eCollection 2016.
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