Background

Definition Chronic fatigue syndrome is characterised by severe, disabling fatigue and other symptoms, including musculoskeletal pain, sleep disturbance, impaired concentration, and headaches. Two widely used definitions of chronic fatigue syndrome (from the US Centers for Disease Control and Prevention1 and from Oxford2—see table) were developed as operational criteria for research. There are two important differences between these definitions. The British criteria insist on the presence of mental fatigue; the American criteria include a requirement for several physical symptoms, reflecting the belief that chronic fatigue syndrome has an underlying immunological or infective pathology.

Incidence/prevalence Community and primary care based studies have reported the prevalence of chronic fatigue syndrome to be 0.2-2.6%, depending on the criteria used.3 4 Systematic population surveys have found similar rates of the syndrome in people of different socioeconomic status, and in all ethnic groups.4 5 Female sex is the only demographic risk factor (relative risk 1.3 to 1.7 depending on diagnostic criteria used).6

Aetiology The cause of chronic fatigue syndrome is poorly understood.

Prognosis Studies of prognosis in chronic fatigue syndrome have focused on people attending specialist clinics, who are likely to have had the condition for longer and to have a poorer outlook. Children with the syndrome seem to have a notably better outcome:54-94% of children show definite improvement (after up to six years' follow up); 20-50% of adults show some improvement in the medium term and only 6% return to premorbid levels of functioning.7 Despite the considerable burden of morbidity associated with chronic fatigue syndrome, there is no evidence of increased …