Elsevier

Sleep Medicine Reviews

Volume 10, Issue 1, February 2006, Pages 63-76
Sleep Medicine Reviews

Theoretical Review
Distinguishing sleepiness and fatigue: focus on definition and measurement

https://doi.org/10.1016/j.smrv.2005.05.004Get rights and content

Summary

Sleepiness and fatigue are two interrelated, but distinct phenomena; observed in a number of psychiatric, medical and primary sleep disorders. Despite their different implications in terms of diagnosis and treatment, these two terms are often used interchangeably, or merged under the more general lay term of ā€˜tiredā€™.

Sleepiness is multidimensional and has many causes (multidetermined) and distinguished from fatigue by a presumed impairment of the normal arousal mechanism. Despite its ubiquity, no clear consensus exits as yet as to what constitutes sleepiness. Definitions of sleepiness, to date, are at best operational definitions, conceptualized so as to produce specific assessment instruments. As a result, while a number of subjective and objective measurement tools have been developed to measure sleepiness, each only captures a limited aspect of an otherwise heterogeneous entity.

Fatigue is an equally complex phenomenon, its nature captured by a number of conceptualizations and definitions. Measures of fatigue have remained subjective, with a ā€˜gold standardā€™ for its measurement remaining elusive. Despite a high prevalence and high degree of morbidity, fatigue has remained a relatively under appreciated symptom, from both a clinical and research point of view.

Introduction

It is not an uncommon experience for a clinician, both in sleep medicine and other fields, to be faced with the patient presenting with a chief complaint of being ā€˜tiredā€™. Such patients, and often their physicians, are usually unaware of the heterogeneity of potential symptoms inherent in this general lay term, not the least of which are the entities of sleepiness and fatigue. As a result, sleepiness and fatigue are two terms often used interchangeably, in both clinical practice and in the research literature, despite the distinct implications each of them has in terms of diagnosis and treatment. In fact, these two symptoms can be difficult to separate. This paper will attempt to outline the nature of both sleepiness and fatigue, with the ultimate goal of providing a framework for defining and evaluating between these two complex phenomena.

Section snippets

Definition and mechanisms

Sleepiness is an ubiquitous phenomenon, experienced not only as a symptom in a number of medical, psychiatric and primary sleep disorders, but also as a normal physiological state by most individuals over any given 24Ā h period. Pathology is inferred both when its presence becomes pervasive (as in narcolepsy) or in its absence (as in insomnia). Alternatively, sleepiness can be considered abnormal when it occurs at inappropriate times, or does not occur when desired. Consequently, no clear

Scope of the problem

Fatigue, like sleepiness, is a highly prevalent phenomenon, associated with a significant level of physical and psychosocial morbidity. It is a commonly reported chief complaint in both primary and specialty medicine. Fatigue is the primary symptom of chronic fatigue syndrome (CFS), and is associated with a number of acute and chronic illnesses, such as rheumatoid arthritis, cancer and multiple sclerosis. It is also prevalent in certain medical treatments, such as radiation or chemotherapy. In

Conclusion

The distinction between fatigue and sleepiness remains somewhat obscure, despite the development of a number of objective and subjective tools for measuring sleepiness, and numerous fatigue scales. Neither sleepiness, nor fatigue is unitary phenomena, each in themselves being complex, heterogeneous phenomena. Sleepiness and fatigue often coexist as a consequence of sleep deprivation, and are often grouped together by such patients under the complaint of being ā€˜tiredā€™. On closer examination,

Glossary

Cronbach's alpha
A statistic that is used to estimate the reliability of a test.
Chronic fatigue syndrome (CFS)
A disorder with fatigue as its major symptom. CFS patients sometimes feel too fatigues to do normal activities or are easily exhausted with no apparent reason. This condition can be months or years.
Electrooculogram (EOG)
A study using electrodes placed around the eyes to detect electrical activities associated with eye movements.
Functional magnetic resonance imaging (fMRI)
An instrument

References (82)

  • R.D. Chervin et al.

    Comparison of the results of the Epworth Sleepiness Scale and the Multiple Sleep Latency Test

    J Psychosom Res

    (1997)
  • T.J. Walter et al.

    Comparison of Epworth Sleepiness Scale scores by patients with obstructive sleep apnea and their bed partners

    Sleep Med

    (2002)
  • R.B. Sangal et al.

    Subjective sleepiness ratings (Epworth sleepiness scale) do not reflect the same parameter of sleepiness as objective sleepiness (maintenance of wakefulness test) in patients with narcolepsy

    Clin Neurophysiol

    (1999)
  • R.D. Chervin

    Sleepiness, fatigue, tiredness, and lack of energy in obstructive sleep apnea

    Chest

    (2000)
  • T. Janjua et al.

    Clinical caveat: prior sleep deprivation can affect the MSLT for days

    Sleep Med

    (2003)
  • R.D. Chervin et al.

    The relation between Multiple Sleep Latency Test findings and the frequency of apneic events in REM and non-REM sleep

    Chest

    (1998)
  • C. Guilleminault et al.

    Determinants of daytime sleepiness in obstructive sleep apnea

    Chest

    (1988)
  • Y. Harrison et al.

    High sleep-ability without sleepiness: the ability to fall asleep rapidly without other signs of sleepiness

    Neurophysiol Clin

    (1996)
  • M.M. Mitler et al.

    Maitenance of wakefulness test: a polysomnographic technique for evaluating treatment efficacy in patients with excessive somnolence

    Electorencephalogr Clin Neurophysiol

    (1982)
  • K. Doghramji et al.

    A normative study of the maintenance of wakefulness test (MWT)

    Electroencephalogr Clin Neurophysiol

    (1997)
  • M. Tiihonen et al.

    Polysomnography and maintenance of wakefulness test as predictors of CPAP effectiveness in obstructive sleep apnea

    Electoencephalogr Clin Neurophysiol

    (1998)
  • R.B. Sangal et al.

    Maintenance of wakefulness test and multiple sleep latency test: measurement of different abilities in patients with sleep disorders

    Chest

    (1992)
  • M.M. Mitler et al.

    The maintenance of wakefulness test normal date by age

    J Psychosom Res

    (2000)
  • J.W. McLaren et al.

    Pupillometry in clinically sleepy patients

    Sleep Med

    (2002)
  • H. Bastuji et al.

    Evoked potentials as a tool for the investigation of human sleep

    Sleep Med Rev

    (1999)
  • C.M. Shapiro

    Chronic fatigue-chronically confusing but growing information

    J Psychosom Res

    (2004)
  • T. Chalder et al.

    Development of a fatigue scale

    J Psychosom Res

    (1993)
  • K.A. Lee et al.

    Validity and reliability of a scale to assess fatigue

    Psychiatry Res

    (1991)
  • E. Ream et al.

    Fatigue in patients with cancer and chronic obstructive airways disease: a phenomenological enquiry

    Int J Nurs Stud

    (1997)
  • J.H. Loge et al.

    Fatigue in the general Norwegian population: normative data and associations

    J Psychosom Res

    (1998)
  • M.M. Andersen et al.

    Illness and disability in Danish chronic fatigue syndrome patients at diagnosis and 5-year follow-up

    J Psychosom Res

    (2004)
  • A.J. Dittner et al.

    The assessment of fatigue: a practical guide for clinicians and researchers

    J Psychosom Res

    (2004)
  • C.M. Shapiro et al.

    Chronic fatigue: listen and measure

    J Psychosom Res

    (2002)
  • E.M. Smets et al.

    The Multidimensional Fatigue Inventory (MFI) psychometric qualities of an instrument to assess fatigue

    J Psychosom Res

    (1995)
  • J.E. Schwartz et al.

    The measurement of fatigue: a new instrument

    J Psychosom Res

    (1993)
  • J.H. Vercoulen et al.

    Dimensional assessment of chronic fatigue syndrome

    J Psychosom Res

    (1994)
  • S.B. Yellen et al.

    Measuring fatigue and other anemia-related symptoms with the Functional Assessment of Cancer Therapy (FACT) measurement system

    J Pain Symptom Manage

    (1997)
  • CM Shapiro et al.

    Development of an adjective checklist to measure five FACES of fatigue and sleepiness: data from a national survey of insomniacs

    J Psychosom Res

    (2002)
  • M. Partinen et al.

    Epidemilogy of sleep disorders

  • L.C. Johnson et al.

    Daytime Sleepiness, performance, mood, nocturnal sleep: the effect of benzodiazepine and caffeine on their relationship

    Sleep

    (1990)
  • M.W. Johns

    Sleep propensity varies with behavior and the situation in which it is measured: the concept of somnificity

    J Sleep Res

    (2002)
  • Cited by (482)

    View all citing articles on Scopus
    1

    Tel.: +1 416 603 5723; fax: +1 416 603 6919.

    2

    Tel.: +1 416 603 5273; fax: +1 416 603 5292.

    View full text