Abstract
Fatigue related to Multiple Sclerosis (MS) is considered a multidimensional symptom, manifesting in several dimensions such as physical, cognitive, and psychosocial fatigue. This study investigated in 264 patients with severe primary MS-related fatigue (median MS duration 6.8 years, mean age 48.1 years, 75% women) whether subgroups can be distinguished based on these dimensions. Subsequently, we tested whether MS-related fatigue consists of a single common unidimensional factor. Subscale scores on four self-reported fatigue questionnaires, including the Checklist of Individual Strength, the Modified Fatigue Impact Scale, the Fatigue Severity Scale and the SF36 vitality, were used in a cluster analysis to identify patients with similar fatigue characteristics. Next, all 54 items were included in exploratory factor analysis to test unidimensionality. Study results show that in patients with a treatment indication for primary MS-related fatigue, fatigue profiles are based on severity and not on the various dimensions of fatigue. The three profiles found, suggested one underlying fatigue dimension, but this could not be confirmed. Factor analysis of all 54 items resulted in 8 factors, confirming the multidimensional construct of the included fatigue questionnaires.
Highlights
There are many definitions of fatigue and over 250 ways to measure fatigue[7]
This fits with the theoretical model of low energy in chronically ill patients described by Lerdal[36]
Fatigue related to Multiple Sclerosis (MS) is considered a multidimensional symptom, manifesting in several dimensions such as physical, cognitive, and psychosocial fatigue
Summary
There are many definitions of fatigue (see Supplementary Information 1 for references regarding Fatigue Definitions) and over 250 ways to measure fatigue[7]. There is no “gold standard” for fatigue, nor is there ever likely to be” This Catch-22 situation has caused many researchers to struggle with the assessment, understanding, etiology and classification of fatigue within different patient groups. The many elements of fatigue in neurological diseases were included in a proposed unified taxonomy for fatigue, including an assessment approach to addressing distinct aspects of fatigue and fatigability in clinical and research settings[6]. Fatigue questionnaires vary greatly regarding the factors examined and may include questions on severity or intensity, duration, momentary perceptions, chronic character, dimensions of fatigue (e.g. mental vs physical), affective meaning and distress (e.g. motivation), impact of fatigue on daily functioning, behavioural interference with activities and ratings of related constructs (e.g. tiredness or sleepiness) (Supplementary Information 2). The presentation of total scores on multidimensional scales results in the loss of information on the underlying individual dimensions[21]
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