ABC of psychological medicine: Fatigue

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Abstract
Causes of fatigue The physiological and psychological mechanisms underlying subjective fatigue are poorly understood. Fatigue may rather be usefully regarded as a final common pathway for a variety of causal factors. These can be split into predisposing, precipitating, and perpetuating factors. Predisposing factorsinclude being female and a history of either fatigue or depression. Precipitating factorsinclude acute physical stresses such as infection with Epstein-Barr virus, psychological stresses such as bereavement, and social stresses such as work problems. Medical conditions that may present with apparently unexplained fatigue General—Anaemia, chronic infection, autoimmune disease, cancer Endocrine disease—Diabetes, hypothyroidism, hypoadrenalism Sleep disorders—Obstructive sleep apnoea and other sleep disorders Neuromuscular—Myositis, multiple sclerosis Gastrointestinal—Liver disease Cardiovascular—Chronic heart disease Respiratory—Chronic lung disease Perpetuating factorsinclude physical inactivity, emotional disorders, ongoing psychological or social stresses, and abnormalities of sleep. These factors should be sought as part of the clinical assessment. Other physiological factors such as immunological abnormalities and slightly low cortisol concentration are of research interest but not clinical value. Diagnoses associated with fatigue Among patients who present with severe chronic fatigue as their main complaint, only a small proportion will be suffering from a recognised medical disease. In no more than 10% of patients presenting with fatigue in primary care is a disease cause found. The rate is even lower in patients seen in secondary care. Fatigue is a major symptom of many psychiatric disorders, but for a substantial proportion of patients with fatigue the symptom remains unexplained or idiopathic. In general, the more severe the fatigue and the larger the number of associated somatic (and unexplained) complaints, then the greater the disability and the greater the likelihood of a diagnosis of depression. Psychiatric diagnoses commonly associated with fatigue Depression Anxiety and panic Eating disorders Substance misuse disorders Somatisation disorder Chronic fatigue syndromes Chronic fatigue syndrome is a useful descriptive term for prominent physical and mental fatigue with muscular pain and other symptoms. It overlaps with another descriptive term, fibromyalgia, that has often been used when muscle pain is predominant but in which fatigue is almost universal. There is also substantial overlap of the diagnoses with other symptom based syndromes, the so called functional somatic syndromes. Diagnostic criteria for chronic fatigue syndrome Inclusion criteria Clinically evaluated, medically unexplained fatigue of at least 6 months' duration that is Of new onset (not life long) Not result of ongoing exertion Not substantially alleviated by rest Associated with a substantial reduction in previous level of activities Occurrence of 4 or more of the following symptoms Subjective memory impairment, sore throat, tender lymph nodes, muscle pain, joint pain, headache, unrefreshing sleep, post-exertional malaise lasting more than 24 hours Exclusion criteria Active, unresolved, or suspected medical disease or psychotic, melancholic, or bipolar depression (but not uncomplicated major depression), psychotic disorders, dementia, anorexia or bulimia nervosa, alcohol or other substance misuse, severe obesity The term myalgic encephalomyelitis (or encephalopathy) has been used in Britain and elsewhere to describe a poorly understood illness in which a prominent symptom is chronic fatigue exacerbated by activity. This is a controversial diagnosis that some regard as simply another name for chronic fatigue syndrome and that others regard as a distinct condition. This article will focus on chronic fatigue syndrome. Prevalence and outcome—Chronic fatigue syndrome can be diagnosed in up to 2% of primary care patients. Untreated, the prognosis is poor, with only about 10% of patients recovering in a two to four years. A preoccupation with medical causes seems to be a negative prognostic factor.

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