Diagnosis guidance A 2023 guidance indicates the following A 2014 Australian review recommended that a period of watchful waiting may be appropriate if there are no major warning signs. 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.
Classification By type Uni- or multi-dimensional Fatigue can be seen as a uni-dimensional phenomenon that influences different aspects of human life. 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. 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. Physical fatigue can be caused by a lack of energy in the muscle, by a decrease of the efficiency of the
neuromuscular junction or by a reduction of the drive originating from the
central nervous system, and can be reversed by rest. The central component of fatigue is triggered by an increase of the level of
serotonin in the central nervous system. During motor activity, serotonin released in synapses that contact
motor neurons promotes
muscle contraction. During high level of motor activity, the amount of serotonin released increases and a spillover occurs. Serotonin binds to extrasynaptic receptors located on the
axonal initial segment of motor neurons with the result that
nerve impulse initiation and thereby muscle contraction are inhibited. 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.
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. Decreased attention can also be described as a more or less decreased
level of consciousness. 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. The
perception of mental fatigue is believed to be modulated by the brain's
reticular activating system (RAS). 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%. Mental fatigue has also been defined from the
cost-benefit model, drawing on influential insights from the current neuroscience literature on how fatigue alters motivation to perform. The model specifies how the reward value, effort costs, and fatigue aspects of task performance converge in the
medial prefrontal cortex to calculate the net motivational value of stimuli and to select appropriate actions.
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". People with
autoimmune diseases including inflammatory rheumatic diseases such as
rheumatoid arthritis,
psoriatic arthritis and primary
Sjögren's syndrome, experience similar fatigue. Other common causes of acute fatigue include
depression and chemical causes, such as
dehydration,
poisoning,
low blood sugar, or
mineral or
vitamin deficiencies. ; :Prolonged fatigue is a self-reported, persistent (constant) fatigue lasting at least one month. ; :Chronic fatigue is a self-reported fatigue lasting at least 6 consecutive months. Chronic fatigue may be either persistent or relapsing. 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. 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.
WHO classification The
World Health Organization's
ICD-11 classification 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. It does not include any fatigue-based psychiatric illness (unless it is accompanied by related psychiatric symptoms).
DSM-5 lists 'fatigue or loss of energy nearly every day' as one factor in diagnosing depression. ==Treatment and management==