Chronic unexplained fatigue.

Fatigue is a common symptom in the community and the commonest associations are with stress or mood disturbance. One in a hundred people complain of unexplained and prolonged fatigue, with half that number meeting the strictest criteria for the chronic fatigue syndrome (CFS). Discrete fatigue syndromes have been described, particularly after Epstein Barr virus infection. The majority of patients with CFS have a syndrome similar to the ICD-10 definition of neurasthenia. Mood and somatoform disorders are common comorbid or differential diagnoses. The prognosis is poor, particularly in patients attending hospitals and those with comorbid psychiatric disorders. The aetiology of both CFS and chronic unexplained fatigue are essentially unknown, perhaps reflecting the heterogenenous natures of both the symptom and syndrome. There is reasonable evidence to suggest that particular infections may trigger both prolonged fatigue and CFS. Maintaining factors are different from triggering factors and include mood and sleep disorders, illness beliefs and behaviours, and possibly inactivity. Treatments aimed at reversing these maintaining factors show promise.