Fatigue

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Fatigue
Other namesExhaustion, weariness, tiredness, lethargy, listlessness
vitamins
Fatigue (medical condition)

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 medical condition.[4]

Fatigue (in the medical sense) is associated with a wide variety of conditions including autoimmune disease, organ failure, chronic pain conditions, mood disorders, heart disease, infectious diseases, and post-infectious-disease states.[5] However fatigue is complex and in some 50% of cases its cause is unknown after one year.[6][7][8]

Fatigue (in the general usage sense of normal tiredness) can include both physical and mental fatigue. Physical fatigue results from muscle fatigue brought about by intense physical activity.[9][10][11] Mental fatigue results from prolonged periods of cognitive activity which impairs cognitive ability. Mental fatigue can manifest as sleepiness, lethargy, or directed attention fatigue,[12] and can also impair physical performance.[13]

Definition

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

Distinguishing features of such 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]

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 to cover variants within the umbrella term of fatigue.[16]

Comparison with other terms

Tiredness

Tiredness which is a normal result of

stress, anxiety, overstimulation and understimulation, jet lag, active recreation, boredom, or lack of sleep is not considered medical fatigue. This is the tiredness described in MeSH Descriptor Data.[17]

Sleepiness

Fatigue is generally considered a longer-term condition than sleepiness (somnolence).[18] Although sleepiness can be a symptom of a medical condition, it usually results from lack of restful sleep, or lack of stimulation.[19] Fatigue is often described as an uncomfortable tiredness, whereas sleepiness can be comfortable and inviting.

Classification

By type

Uni- or multi-dimensional

Fatigue can be seen as a uni-dimensional phenomenon that influences different aspects of human life.[20][21] 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.[22]

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

axonal initial segment of motor neurons with the result that nerve impulse initiation and thereby muscle contraction are inhibited.[27]

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.[28]

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.[29]

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

level of consciousness.[30] In any case, this can be dangerous when performing tasks that require constant concentration, such as operating large vehicles. For instance, a person who is sufficiently somnolent may experience microsleep. However, objective cognitive testing can be used to differentiate the neurocognitive deficits of brain disease from those attributable to tiredness.[citation needed
]

The

]

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%.[31]

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".[32][33][34]

People with

Sjögren's syndrome, experience similar fatigue.[14][35][36]

Attempts have been made to isolate causes of central nervous system fatigue.

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.[37]

Other common causes of acute fatigue include

low blood sugar, or mineral or vitamin
deficiencies.

Prolonged

Prolonged fatigue is a self-reported, persistent (constant) fatigue lasting at least one month.[medical citation needed]

Chronic

Chronic fatigue is a self-reported fatigue lasting at least 6 consecutive months. Chronic fatigue may be either persistent or relapsing.[38] Chronic fatigue is a symptom of many chronic illnesses and of idiopathic chronic fatigue.

By effect

Fatigue can have significant negative impacts on quality of life.[39][40] 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, chronic fatigue syndrome, and rheumatoid arthritis.[14]

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[41] 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.[42] The ICD-11 does not include any fatigue-based psychiatric illness (unless it is accompanied by related psychiatric symptoms).[43][44] DSM-5 lists 'fatigue or loss of energy nearly every day' as one factor in diagnosing depression.[45]

Measurement

Fatigue is currently measured by many different self-measurement surveys.[46] One example is the Fatigue Severity Scale.[47][48][49] There is no consensus on best practice,[50] 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,[51] but the project was stopped in 2016.[52]

Causes

Sleep disturbance

Fatigue can often be traced to poor sleep habits.[53] Sleep deprivation and disruption is associated with subsequent fatigue.[54][55] Sleep disturbances due to disease may impact fatigue.[56][57]

Drug use

Caffeine and alcohol can cause fatigue.[58]

Medications

Fatigue may be a side effect of certain

radiotherapy
.

Obesity

Obesity correlates with higher fatigue levels and incidence.[59][60][61][60]

Psychological stress and conditions

Depression and 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 illnesses;

  • alcohol use disorder[77]

Mental illnesses;

Other;

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).[80][81][82][83][84][85] The ICD-11 MG22 definition of fatigue [86] captures both types of fatigue; it includes fatigue that "occur[s] in the absence of... exertion... as a symptom of health conditions."

Unknown

A 2009 study concluded that about 50% of people who have fatigue do not receive a diagnosis that could explain the fatigue after a year with the condition.[6] [7]

Mechanisms

The mechanisms that cause fatigue are not well understood.[22] Several mechanisms may be in operation within a patient,[87] with the relative contribution of each mechanism differing over time.[14]

Some mechanisms proposed as active in fatigue are:

Inflammation

Inflammation distorts neural chemistry, brain function and functional connectivity across a broad range of brain networks,[88] and has been linked to many types of fatigue.[62][89] Findings implicate neuroinflammation in the etiology of fatigue in autoimmune and related disorders.[14][62] Low-grade inflammation may cause an imbalance between energy availability and expenditure.[90]

ME/CFS.[93]

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

Sjögren's syndrome patients with high fatigue, when compared with those with low fatigue, had significantly higher plasma concentrations of HSP90α, and a tendency to higher concentrations of HSP72.[94] A small 2020 study of Crohn’s disease patients found that higher fatigue visual analogue scale (fVAS) scores correlated with hgher HSP90α levels.[95] A related small 2012 trial investigating if application of an IL-1 receptor antagonist (anakinra) would reduce fatigue in primary Sjögren's syndrome patients was inconclusive.[96][97][98]

Reduced brain connectivity

Fatigue has been correlated with reductions in structural and functional connectivity in the brain.[99] This has included in post-stroke,[100] MS,[101] NMOSD and MOG,[15] and ME/CFS.[102] This was also found for fatigue after brain injury,[103] including a significant linear correlation between self-reported fatigue and brain functional connectivity.[104] (Areas of the brain for which there is evidence of relation to fatigue are the thalamus and middle frontal cortex,[104] fronto-parietal and cingulo-opercular,[103] and default mode network, salience network, and thalamocortical loop areas.[99][105])

Prevalence

2023 guidance stated fatigue prevalence is between 4.3% and 21.9%. Prevalence is higher in women than men.[106][107]

A 2021 German study found that fatigue was the main or secondary reason for 10–20% of all consultations with a primary care physician.[108]

Diagnosis

The overall goal in diagnosis is to identify and rule out any treatable conditions. This is done by considering

  • the person's medical history, any other symptoms present.
  • evaluation of the qualities of the fatigue itself. Identifiable patterns to the fatigue can include being more tired at certain times of day, whether fatigue increases throughout the day, and whether fatigue is reduced after taking a nap.
  • sleep patterns. These can be examined by enquiring about quality of sleep, the emotional state of the person, sleep pattern, and stress level. The amount of sleep, the hours that are set aside for sleep, and the number of times that a person awakens during the night are important. A sleep study may be ordered to rule out a sleep disorder.
  • depression and other psychological conditions.
  • substance use disorders, and use of caffeine and alcohol.
  • poor diet.
  • lack of
    physical exercise
    (which paradoxically increases fatigue).

Further tests may include

eye bags, a combination which can correlate with fatigue.[110]

A 2009 study concluded about 50% of people who have fatigue receive a diagnosis that could explain the fatigue after a year with the condition. In those people who have a possible diagnosis, musculoskeletal (19.4%) and psychological problems (16.5%) are the most common. Definitive physical conditions were only found in 8.2% of cases.[6]

2023 guidance stated

  • 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 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.[106]

A German 2016 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. Extensive diagnostic testing in fatigued patients in primary care might lead to false-positive tests and rarely helped detect serious diseases if fatigue occurred as an isolated symptom without additional abnormalities in the medical history and in the clinical examination.[111]

A 2014 Australian review recommended that a period of watchful waiting may be appropriate if there are no major warning signs.[112]

Somatic symptom disorder may be diagnosed,[113] in which the patient is overfocused on a physical symptom, such as fatigue, that may or may not be explained by a medical condition.[114][115][116]

Treatment and Management

Management may include the following;

Lifestyle changes

Fatigue may be reduced by reducing obesity, caffeine and alcohol intake,[117] pain and sleep disturbance, and by improving mental well-being.[118][14] Aerobic exercise may reduce fatigue.[119]

Review of existing medications

Medications may be evaluated for side effects that contribute to fatigue[120]

better source needed] and the interactions of medications are complex.[non-primary source needed][122]

Medications used to treat fatigue

The UK

Mental health tools

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.[138] CBT has been found useful.[139]

Avoidance of body heat

Fatigue in

Qigong and Tai Chi

Qigong and Tai chi have been postulated as helpful to reduce fatigue, but the evidence is of low quality.[151][152][153]

Intermittent fasting

A small 2022 study found both physical and mental fatigue were significantly reduced after three months of 16:8 intermittent fasting.[154]

Vagus nerve stimulation

A small 2023 study showed possible efficacy of

Sjogren's patients.[92]

Possible purposes of fatigue

Body resource management purposes

Fatigue has been posited as a bio-psycho-physiological state reflecting the body's overall strategy in resource (energy) management. Fatigue may occur when the body wants to limit resource utilisation ("rationing") in order to use resources for healing (part of

sickness behaviour)[95] or conserve energy for a particular current or future anticipated need, including a threat.[14]

Evolutionary purposes

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.[87]

Needs for research

Whilst fatigue may vary considerably by person, it may be possible to identify distinguishing characteristics linking it to different causes.[155] For instance ME/CFS includes post-exertional malaise,[156] which other fatigues do not. ME/CFS fatigue seems to be continual (24/7) whilst autoimmune related fatigues are intermittent. MS fatigue includes the particular "lassitude' form.[32] A 2010 study found that Sjogrens 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.[157]

The possible influence of personal psychological factors on fatigue formation is another possible research area.[158]

See also

References

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Further reading

External links