Fatigue may be a symptom of almost any medical condition. For the purpose of this topic, the differentials discussed concentrate on people presenting with fatigue or where fatigue is the only symptom. Conditions in which fatigue may not necessarily be an initial complaint, but is still regarded as a markedly significant and debilitating symptom, are also included.
Summary
Definition
There are numerous definitions and classifications of fatigue, reflecting the multitude of interpretations, depending on being a patient, a physician, a biologist, or a physiologist. A common and practical definition defined fatigue as a sensation of exhaustion during or after usual activities, or a feeling of inadequate energy to begin these activities.[1]
Epidemiology
Primary-care-based surveys have shown that between 11% and 33% of patients report significant fatigue, resulting in approximately 7 million office visits per year in the US. Fatigue is also a common complaint in the general population, with a prevalence between 4.3% and 21.9%.[2] [3] [4] [5] [6] [7]
In the primary care setting, a medical or psychiatric diagnosis is found in the majority of patients presenting with fatigue (at least two-thirds).[8] [9] [10] [11] [12] A Dutch study identified a specific diagnosis in 63% of patients presenting to a general practitioner with general weakness or tiredness for any length of time.[11] One study identified the most common diagnoses, in descending order, as viral illness, upper respiratory infection, iron-deficiency anemia, acute bronchitis, adverse effects of a medical agent in the proper dose, and depression or other mental disorder.[13] The most frequent psychiatric illnesses included major depression, panic disorder, and somatization disorder. A systematic review and meta-analysis of studies reporting on the differential diagnosis of tiredness in primary care found serious somatic disease was a rare cause. The prevalences of the following causes were found to be: anemia (2.8%); malignancy (0.6%); serious somatic disease (4.3%); depression (18.5%).[14]
Classification
Fatigue can be divided into categories based on origin, attribution, and duration of symptoms. The origin of fatigue may be:
- Central (brain-derived)
- Peripheral (usually a neuromuscular origin).
It may be attributed to:[8]
- 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).
The duration of symptoms may refer to:
- Recent fatigue (symptoms lasting <1 month)
- Prolonged fatigue (symptoms lasting >1 month)
- Chronic fatigue (symptoms lasting >6 months).
When unexplained, clinically evaluated chronic fatigue can be separated into myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and idiopathic chronic fatigue.[18] [19] ME/CFS represents a small subset of those who report actual chronic fatigue. Even in patients with fatigue of 6 months or longer in duration, the prevalence is <40%. European studies have shown that patients with fatigue lasting longer than 6 months were given a diagnosis of ME/CFS in up to one third of cases.[9] [13] [20] [21] [22] The US Institute of Medicine has clustered several key symptoms associated with ME/CFS, and has proposed the term "systemic exertion intolerance disease" (SEID) as an alternative to ME/CFS.[23]
Citations
National Institute for Health and Care Excellence. Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management. Oct 2021 [internet publication].[Full Text]
Centers for Disease Control and Prevention. Myalgic encephalomyelitis/chronic fatigue syndrome: clinical overview of ME/CFS. May 2024 [internet publication].[Full Text]
Cornuz J, Guessous I, Favrat B. Fatigue: a practical approach to diagnosis in primary care. CMAJ. 2006 Mar 14;174(6):765-7.[Abstract][Full Text]
Hamilton W, Watson J, Round A. Investigating fatigue in primary care. BMJ. 2010;341:c4259.[Abstract]
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