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.
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.
Fatigue is a common complaint in the general population, with a prevalence between 4.3% and 21.9%. In the US, primary care-based surveys have shown that between 11% and 33% of patients report significant fatigue, resulting in approximately 7 million surgery visits per year.
In the primary care setting, a medical or psychiatric diagnosis is found in the majority of patients presenting with recent fatigue (at least two-thirds). A Dutch study identified a specific diagnosis in 63% of patients presenting to general practitioners with general weakness or tiredness for any length of time. One study identified the most common diagnoses, in descending order, as 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. The most frequent psychiatric illnesses included major depression, panic disorder, and somatisation 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: anaemia (2.8%); malignancy (0.6%); serious somatic disease (4.3%); depression (18.5%).
Fatigue can be divided into categories based on origin, attribution, and duration of symptoms. The origin of fatigue may be:
Peripheral (usually a neuromuscular origin).
It may be attributed to:
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 chronic fatigue syndrome (also known as myalgic encephalomyelitis [ME]) and idiopathic chronic fatigue. Chronic fatigue syndrome 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 chronic fatigue syndrome in up to one third of cases. The US Institute of Medicine has clustered several key symptoms associated with chronic fatigue syndrome, and has proposed the term ‘systemic exertion intolerance disease’ (SEID) as an alternative to chronic fatigue syndrome.
- Insomnia disorder
- Iron-deficiency anaemia
- Iron deficiency without anaemia
- Chronic heart failure
- Diabetes mellitus
- EBV infection
- Influenza infection
- Coronavirus disease 2019 (COVID-19)
- Long COVID
- Medicine-induced fatigue
- Alcohol dependence
- Drug dependence
- HIV infection
- Acute myocardial ischaemia
- Atrial fibrillation
- Obstructive sleep apnoea/hypopnoea syndrome (OSAHS)
- Obesity hypoventilation syndrome (OHS)
- Restless legs syndrome
- Coeliac disease
- Addison's disease
- Myelodysplastic syndrome
- Chronic myeloid leukaemia
- Non-Hodgkin's lymphoma
- Hodgkin's lymphoma
- Cytomegalovirus infection
- Lyme disease
- Chronic renal disease
- Multiple sclerosis
- Parkinson's disease
- Vitamin D deficiency (osteomalacia)
- Systemic lupus erythematosus
- Primary biliary cirrhosis
- Underlying malignancy (non-lymphoma)
- Chronic fatigue syndrome (myalgic encephalomyelitis)/systemic exertion intolerance disease
- Chronic idiopathic fatigue
- Heavy metal toxicity
- Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s
- Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management
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