The assessment of fatigue: A practical guide for clinicians and researchers
Introduction
Although often identified as a sign or symptom of a disease state or side effect or treatment, fatigue is essentially a subjective experience. It has largely defied efforts to conceptualise or define it in a way that separates it from normal experiences such as tiredness or sleepiness. Emphasis is usually given to the degree and persistence of such experiences in the absence of any excessive expenditure of energy or effort as cause. Thus, fatigue is typically defined as extreme and persistent tiredness, weakness or exhaustion—mental, physical or both. Fatigue is common in the general population [1], [2] and is the defining feature of chronic fatigue syndrome (CFS). However, it is also an important feature of a wide range of other conditions including physical disease such as cancer, neurological disease such as multiple sclerosis (MS) and Parkinson's disease and psychiatric disorders such as depression. In these and other conditions, fatigue can be a major source of disablement and is often reported by patients as being amongst their most severe and distressing symptoms [3], [4], [5], [6], [7]. Despite this, fatigue has typically been ignored in the assessment of symptom severity or outcome in many of the diseases in which it is found. Consequently, we know little about the phenomenology of fatigue in these conditions, quite apart from their epidemiology and aetiology. Finally, fatigue is often neglected as a target for treatment, perhaps because it typically appears unrelated to the severity of the central disease process.
Progress in research and improved management depends on having reliable and valid methods of assessment that reflect the problems reported by patients. With the growing recognition of fatigue as a major clinical problem in many conditions, there has been a proliferation of measures of fatigue, often referred to by synonyms or abbreviations shared with other scales. Although all purport to assess fatigue, being self-report scales, the information derived depends on the questions being asked. These will be based on the scale developer's own conceptualisation of fatigue and will in turn be answered by the respondent based on his or her own interpretation. This means that different scales may be measuring fundamentally different aspects of the fatigue experience or even potentially distinct constructs. In addition, where an instrument has been developed specifically to measure fatigue in one clinical condition, its use in other patient groups may not be justified if the fatigue experience differs from group to group.
A researcher or clinician wishing to measure fatigue in their patients needs to ensure that the instrument chosen measures the right aspect of fatigue for their purposes, in a way that meets the requirements of their study and does so both reliably and validly. However, choice of the most appropriate measure is far from straightforward. The purpose of the present review is to describe the range of instruments available and to provide guidance on choosing a scale for a specific use. It does not seek to compare scales directly although published studies that have sought to do so will be discussed.
Section snippets
Procedure
The scales included in this article are the result of a bibliographic search of English language publications indexed in Medline (1966 to March 2003), EMBASE (1980 to March 2003) and PsycINFO (1974 to March 2003). Searches were based on the main Medical Library Subject Heading (MESH) term “fatigue” (synonym “lassitude,” previously “tiredness”). The scope of this term is defined as “the state of weariness following a period of exertion, mental or physical characterised by a decreased capacity
Recommendations
Fatigue assessment depends on a clear understanding of the phenomenology and aetiology of fatigue within a condition. In developing fatigue scales, there is a “catch-22” situation: before a concept can be measured, it must be defined, and before a definition can be agreed, there must exist an instrument for assessing phenomenology. There is unfortunately no “gold standard” for fatigue, nor is there ever likely to be.
There are a number of issues to be considered in choosing a particular scale
Conclusion
There is clearly much to be done in the development of new scales and in the further validation of those already in existence. Even basic data on reliability are missing on many scales; few provide evidence on sensitivity to change or suggest cutoff scores for identifying levels of clinical caseness. This latter shortcoming is particularly significant given the prevalence of fatigue within the general population. Although different scales are often used for cross validation, there have been
Acknowledgements
This work was supported by a grant from the Parkinson's Disease Society (UK).
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