Fatigue

Fatigue describes a state of tiredness (which is not sleepiness), exhaustion^[1] or loss of energy.^[2][3]

In general usage, fatigue often follows prolonged physical or mental activity. When fatigue occurs independently of physical or mental exertion, or does not resolve after rest or sleep, it may have other causes, such as a

Fatigue in a medical context is used to cover experiences of low energy that are not caused by normal life.[2]^[3]

A 2021 review proposed a definition for fatigue as a starting point for discussion: "A multi-dimensional phenomenon in which the biophysiological, cognitive, motivational and emotional state of the body is affected resulting in significant impairment of the individual's ability to function in their normal capacity".^[14]

Another definition is that fatigue is "a significant subjective sensation of weariness, increasing sense of effort, mismatch between effort expended and actual performance, or exhaustion independent from medications, chronic pain, physical deconditioning, anaemia, respiratory dysfunction, depression, and sleep disorders".^[15]

Terminology

The use of the term "fatigue" in medical contexts may carry inaccurate connotations from the more general usage of the same word. More accurate terminology may also be needed for variants within the umbrella term of fatigue.^[16]

Comparison with other terms

Tiredness

Tiredness which is a normal result of

Sleepiness refers to a tendency to fall asleep, whereas fatigue refers to an overwhelming sense of tiredness, lack of energy, and a feeling of exhaustion. Sleepiness and fatigue often coexist as a consequence of sleep deprivation.[18] However sleepiness and fatigue may not correlate.^[19] Fatigue is generally considered a longer-term condition than sleepiness (somnolence).^[20]

Features

Common features

Distinguishing features of medical fatigue include

• unpredictability,
• not linking fatigue to an obvious cause, such as a physical exertion,
• variability in severity,
• fatigue being relatively profound/overwhelming, and having extensive impact on daily living,
• lack of improvement with rest,
• where an underlying disease is present, the quantum of fatigue often does not correlate with the severity of the underlying disease.^{[14][21][22][23]}

Characteristics by cause

Differentiating characteristics of fatigue that may help identify the possible cause of fatigue include

• Post-exertional malaise; a common feature of ME/CFS fatigue,^[24] but not a feature of other fatigues.
• Increased by heat or cold; MS fatigue is in many cases effected in this way.^[25][26]
• Remission; MS fatigue may reduce during periods of other MS symptom remission.^[27][28] ME/CFS may also have lower periods of activity.^[29]
• Cognitive declines; sleep deprivation causes cognitive and neurobehavioral effects including unstable attention and slowing of response times.^[30]
• Intermittency; Fatigues often vary in how and when they occur. For instance ME/CFS symptoms can fluctuate during the day, from day to day, and over longer periods.^[29] However some fatigues (RA, cancer fatigue^[31]) seem to often be continual (24/7) whilst others (MS, Sjögren's, lupus, brain injury^[32]) are often intermittent.^[33] A 2010 study found that Sjögren's patients reported fatigue after rising, an improvement in mid-morning, and worsening later in the day, whereas lupus (SLE) patients reported lower fatigue after rising followed by increasing fatigue through the day.^[34] The pace of onset may be a related differentiating factor; MS fatigue can have abrupt onset.^[35]

Some people may have multiple causes of fatigue.

Classification

By type

Uni- or multi-dimensional

Fatigue can be seen as a uni-dimensional phenomenon that influences different aspects of human life.^[36][37] It can be multi-faceted and broadly defined, making understanding the causes of its manifestations especially difficult in conditions with diverse pathology including autoimmune diseases.^[38]

A 2021 review considered that different "types/subsets" of fatigue may exist and that patients normally present with more than one such "type/subset". These different "types/subsets" of fatigue may be different dimensions of the same symptom, and the relative manifestations of each may depend on the relative contribution of different mechanisms. Inflammation may be the root causal mechanism in many cases.^[14]

Physical

Physical fatigue, or

Muscle strength testing can be used to determine the presence of a neuromuscular disease, but cannot determine its cause. Additional testing, such as electromyography, can provide diagnostic information, but information gained from muscle strength testing alone is not enough to diagnose most neuromuscular disorders.^[44]

Mental

Mental fatigue is a temporary inability to maintain optimal cognitive performance. The onset of mental fatigue during any cognitive activity is gradual, and depends upon an individual's cognitive ability, and also upon other factors, such as sleep deprivation and overall health.

Mental fatigue has also been shown to decrease physical performance.^[12] It can manifest as somnolence, lethargy, directed attention fatigue, or disengagement. Research also suggests that mental fatigue is closely linked to the concept of ego depletion, though the validity of the concept is disputed. For example, one pre-registered study of 686 participants found that after exerting mental effort, people are likely to disengage and become less interested in exerting further effort.^[45]

Decreased attention can also be described as a more or less decreased

Fatigue impacts a driver's reaction time, awareness of hazards around them and their attention. Drowsy drivers are three times more likely to be involved in a car crash, and being awake over 20 hours is the equivalent of driving with a blood-alcohol concentration level of 0.08%.[55]

Neurological fatigue

People with multiple sclerosis experience a form of overwhelming tiredness that can occur at any time of the day, for any duration, and that does not necessarily recur in a recognizable pattern for any given patient, referred to as "neurological fatigue", and often as "multiple sclerosis fatigue" or "lassitude".^[56][57][58]

People with

By timescale

Acute

Acute fatigue is that which is temporary and self-limited. Acute fatigue is most often caused by an infection such as the common cold and can be cognized as one part of the sickness behavior response occurring when the immune system fights an infection.^[59]

Other common causes of acute fatigue include

Prolonged fatigue is a self-reported, persistent (constant) fatigue lasting at least one month.[60]^[61]

Chronic

Chronic fatigue is a self-reported fatigue lasting at least 6 consecutive months. Chronic fatigue may be either persistent or relapsing.^[62] Chronic fatigue is a symptom of many chronic illnesses and of idiopathic chronic fatigue.^{[medical citation needed]}

By effect

Fatigue can have significant negative impacts on quality of life.^[63][64] Profound and debilitating fatigue is the most common complaint reported among individuals with autoimmune disease, such as systemic lupus erythematosus, multiple sclerosis, type 1 diabetes, celiac disease, Myalgic Encephalomyelitis/chronic fatigue syndrome, and rheumatoid arthritis.^[14]

Fatigue has been described by sufferers as 'incomprehensible' due to its unpredictable occurrence, lack of relationship to physical effort and different character as compared to tiredness.^[65]

Fatigue that dissociates by quantum with disease activity represents a large health economic burden and unmet need to patients and to society.^[14]

Formal classification

The World Health Organization's ICD-11 classification^[66] includes a category MG22 Fatigue (typically fatigue following exertion but sometimes may occur in the absence of such exertion as a symptom of health conditions), and many other categories where fatigue is mentioned as a secondary result of other factors.^[67] It does not include any fatigue-based psychiatric illness (unless it is accompanied by related psychiatric symptoms).^[68][69]

DSM-5 lists 'fatigue or loss of energy nearly every day' as one factor in diagnosing depression.^[70]

Measurement

Fatigue is currently measured by many different self-measurement surveys.^[71] One example is the Fatigue Severity Scale.^[72][73][74] There is no consensus on best practice,^[75] and the existing surveys do not capture the intermittent nature of some forms of fatigue.

Nintendo announced plans for a device to possibly quantitatively measure fatigue in 2014,^[76] but the project was stopped in 2016.^[77]

Causes

Unknown

In up to a third of fatigue primary care cases no medical or psychiatric diagnosis is found.^[6][7][8] Tiredness is a common medically unexplained symptom.^[7]

Sleep disturbance

Fatigue can often be traced to poor sleep habits.^[78] Sleep deprivation and disruption is associated with subsequent fatigue.^[79][80] Sleep disturbances due to disease may impact fatigue.^[81][82]

Medications

Fatigue may be a side effect of certain

Psychological stress and conditions

Adverse life events have been associated with fatigue.^[14]

Association with diseases and illnesses

Fatigue is often associated with diseases and conditions. Some major categories of conditions that often list fatigue as a symptom include physical diseases, substance use illness, mental illnesses, and other diseases and conditions.

Physical diseases

• UCTD;^[86] this population's primary concern is fatigue;^[38][87]
• hemochromatosis;^{[medical citation needed}
  ]
• brain injury;^[88][89]
• cancer fatigue;^[90]
• Covid-19 and long Covid;^[91]
• developmental disorders such as autism spectrum disorder;^[92]
• diabetes mellitus, hypothyroidism and Addison's disease;^[93]
• fibromyalgia;^{[medical citation needed]}
• heart attack;^[94]
• HIV;^{[medical citation needed]}
• inborn errors of metabolism such as fructose malabsorption;^[95][96]
• infectious diseases such as infectious mononucleosis or tuberculosis;^[93]
• irritable bowel syndrome;^{[medical citation needed]}
• chronic renal failure;^[93]
• leukemia or lymphoma;^{[medical citation needed]}
• liver failure or liver diseases, e.g., hepatitis;^[93][22]
• Lyme disease;^{[medical citation needed]}
• postural orthostatic tachycardia syndrome (POTS) and post-concussion syndrome;^{[medical citation needed}
  ]
• physical trauma and other pain-causing conditions, such as arthritis;^{[medical citation needed}
  ]
• sleep deprivation or sleep disorders, e.g. sleep apnea;^[93]
• stroke;^{[medical citation needed]}
• thyroid disease such as hypothyroidism;^{[medical citation needed]}

Substance use illnesses

• alcohol use disorder;^[97]

• anxiety disorders, such as generalized anxiety disorder;^[98]
• depression;^[99][14]
• eating disorders, which can produce fatigue due to inadequate nutrition;^{[medical citation needed]}
• Gulf War syndrome;^{[medical citation needed]}

Other

• myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS);^[97]
• idiopathic chronic fatigue, a term used to describe chronic fatigue which does not have symptoms of ME/CFS.^[100][101] However ICF does not have a dedicated diagnostic code in the World Health Organization's ICD-11 classification.^[102]

Primary vs. secondary

In some areas it has been proposed that fatigue be separated into primary fatigue, caused directly by a disease process, and ordinary or secondary fatigue, caused by a range of causes including exertion and also secondary impacts on a person of having a disease (such as disrupted sleep).^{[103][104][105][106][107][108]} The ICD-11 MG22 definition of fatigue^[109] captures both types of fatigue; it includes fatigue that "occur[s] in the absence of... exertion... as a symptom of health conditions."^{[medical citation needed]}

Obesity

Obesity correlates with higher fatigue levels and incidence.^{[110][111][112]}

Drug use

Caffeine and alcohol can cause fatigue.^[113]

Somatic symptom disorder

In somatic symptom disorder^[114] the patient is overfocused on a physical symptom, such as fatigue, that may or may not be explained by a medical condition.^{[115][116][117]}

Scientifically unsupported causes

The concept of adrenal fatigue is often raised in media but no scientific basis has been found for it.^{[118][119][120]}

Mechanisms

The mechanisms that cause fatigue are not well understood.^[38] Several mechanisms may be in operation within a patient,^[121] with the relative contribution of each mechanism differing over time.^[14]

Some mechanisms proposed as active in fatigue are inflammation, heat shock proteins and reduced brain connectivity.

Inflammation

Inflammation distorts neural chemistry, brain function and functional connectivity across a broad range of brain networks,^[122] and has been linked to many types of fatigue.^[38][123] Findings implicate neuroinflammation in the etiology of fatigue in autoimmune and related disorders.^[14][38] Low-grade inflammation may cause an imbalance between energy availability and expenditure.^[124]

The inflammation model may have difficulty in explaining the "unpredictability" and "variability" (i.e. appearing intermittently during the day, and not on all days) of the fatigue associated with inflammatory rheumatic diseases and autoimmune diseases (such as multiple sclerosis).^[14]

Heat shock proteins

A small 2016 study found that primary

Fatigue has been correlated with reductions in structural and functional connectivity in the brain.[133] This has included in post-stroke,^[134] MS,^[135] NMOSD and MOG,^[15] and ME/CFS.^[136] This was also found for fatigue after brain injury,^[137] including a significant linear correlation between self-reported fatigue and brain functional connectivity.^[138]

Areas of the brain for which there is evidence of relation to fatigue are the thalamus and middle frontal cortex,^[138] fronto-parietal and cingulo-opercular,^[137] and default mode network, salience network, and thalamocortical loop areas.^[133][139]

Prevalence

2023 guidance stated fatigue prevalence is between 4.3% and 21.9%. Prevalence is higher in women than men.^[6][140]

A 2021 German study found that fatigue was the main or secondary reason for 10–20% of all consultations with a primary care physician.^[141]

A large study based on the 2004 Health and Retirement Study (HRS), a biennial longitudinal survey of US adults aged 51 and above, with mean age 65, found that 33% of women and 29% of men self-reported fatigue.^[142]

Diagnosis

This section needs more primary sources. Please review the contents of the section and add the appropriate references if you can. Unsourced or poorly sourced material may be challenged and removed. Find sources: "Fatigue" – news · newspapers · books · scholar · JSTOR (April 2024)

2023 guidance^[6] stated the following:

• in the primary care setting, a medical or psychiatric diagnosis is found in at least two-thirds of patients;
• the most common diagnoses are viral illness, upper respiratory infection, iron-deficiency anaemia, acute bronchitis, adverse effects of a medical agent in the proper dose, and depression or other mental disorder, such as panic disorder, and somatisation disorder;
• the origin of fatigue may be central, brain-derived, or peripheral, usually of a neuromuscular origin—it may be attributed to physical illness, psychological (e.g., psychiatric disorder), social (e.g., family problems), and physiological factors (e.g., old age), occupational illness (e.g., workplace stress);
• when unexplained, clinically evaluated chronic fatigue can be separated into ME/CFS and idiopathic chronic fatigue.^[6]

A 2016 German review found that

• about 20% of people complaining of tiredness to a GP (general practitioner) suffered from a depressive disorder.
• anaemia, malignancies and other serious somatic diseases were only very rarely found in fatigued primary care patients, with prevalence rates hardly differing from non-fatigued patients.
• if fatigue occurred in primary care patients as an isolated symptom without additional abnormalities in the medical history and in the clinical examination, then extensive diagnostic testing rarely helped detect serious diseases. Such testing might also lead to false-positive tests.^[143]

A 2014 Australian review recommended that a period of watchful waiting may be appropriate if there are no major warning signs.^[144]

A 2009 study found that about 50% of people who had fatigue received a diagnosis that could explain the fatigue after a year with the condition. In those people who had a possible diagnosis, musculoskeletal (19.4%) and psychological problems (16.5%) were the most common. Definitive physical conditions were only found in 8.2% of cases.^[145]

Treatment and Management

Management may include review of existing medications, and other factors and methods explained below.

Review of existing medications

Medications may be evaluated for side effects that contribute to fatigue^[146]

CBT has been found useful for fatigue.^[164]

Improved sleep

Improving sleep can reduce fatigue.^[165][166]

Lifestyle changes

Fatigue may be reduced by reducing obesity, caffeine and alcohol intake,^{[citation needed]} pain and sleep disturbance, and by improving mental well-being.^[167][14] Aerobic exercise may reduce fatigue.^[168] Caffeine is used by many people to manage fatigue, but may have complex effects including later tiredness.^{[169][166][170][171]}

Avoidance of body heat

Fatigue in

Qigong and Tai chi have been postulated as helpful to reduce fatigue, but the evidence is of low quality.^{[183][184][185]}

Intermittent fasting

A small 2022 study found both physical and mental fatigue were significantly reduced after three months of 16:8 intermittent fasting.^[186]

Vagus nerve stimulation

A small 2023 study showed possible efficacy of

It has been posited that fatigue had evolutionary benefits in making more of the body's resources available for healing processes, such as immune responses, and in limiting disease spread by tending to reduce social interactions.[121]

Needs for research

Differentiating characteristics of fatigue due to different causes

Whilst fatigue may vary considerably by person, it may be possible to identify distinguishing characteristics linking it to different causes.^{[187][33][188]}

Impact of phsychological factors

The possible influence of personal psychological factors on fatigue formation is another possible area of research.^[189]

See also

References

Further reading

• ISBN 978-3-88221-616-5
  . (Philosophical essay about fatigue as a sociological problem and symptom).
  • Danish edition: Træthedssamfundet. Møller, 2012,
    ISBN 978-87-994043-7-7
    .
  • Dutch edition: De vermoeide samenleving. van gennep, 2012,
    ISBN 978-94-6164-071-0
    .
  • Italian editions: La società della stanchezza. nottetempo, 2012,
    ISBN 978-88-7452-345-0
    .
  • Korean edition: 한병철 지음 | 김태환 옮김. Moonji, 2011,
    ISBN 978-89-320-2396-0
    .
  • Spanish edition: La sociedad del cansancio. Herder Editorial, 2012,
    ISBN 978-84-254-2868-5
    .

External links

Wikiquote has quotations related to Fatigue.

Wikimedia Commons has media related to Fatigue.

• Fatigue – Information for Patients, U.S. National Cancer Institute