Box 1: Criteria for CFS (as defined by Fukuda et al., 1994) (ref 44)

These have become the most internationally accepted criteria for the diagnosis of CFS for research and surveillance purposes and have proved remarkably robust in various settings. However, clinicians must recognize that there are no agreed or validated clinical criteria for use in clinical practice. The constraints of the existing definitions designed for research or surveillance need modification in this setting, especially in respect of allowing for co-morbid conditions, for example.

Fukuda criteria:

1. Clinically evaluated, unexplained, persistent or relapsing chronic fatigue that:

• is of new or definite onset (ie has not been life-long)
• is not the result of ongoing exertion
• is not substantially alleviated by rest
• results in substantial reduction in occupational, educational, social or personal activities.
  

2. The concurrent occurrence of four or more of the following symptoms, all of which must have persisted or recurred during six or more consecutive months of illness and must not have pre-dated the fatigue:

• self-reported impairment in short-term memory or concentration, severe enough to cause substantial reduction in previous levels of activities
• sore throat
• tender cervical or axillary lymph nodes
• muscle pain
• multi-joint pain without joint swelling or redness
• headaches of a new type, pattern or severity
• unrefreshing sleep
• post-exertional malaise lasting more than 24 hours.

3. The following conditions exclude a patient from the diagnosis of unexplained chronic fatigue:

• Any active medical condition that may explain the presence of chronic fatigue, such as untreated hypothyroidism, sleep apnoea, narcolepsy and the side-effects of medication.
• Any previously diagnosed medical condition whose continued activity might explain the chronic fatiguing illness, such as previously treated malignancies and unresolved cases of Hepatitis B or C infection.
• Any past or current diagnosis of a major depressive disorder, with psychotic or melancholic features, bipolar affective disorders, schizophrenia of any subtype, delusional disorders of any subtype, dementias of any subtype, anorexia nervosa, or bulimia nervosa.
• Alcohol or other substance abuse within two years before the onset of the chronic fatigue and at any time afterward.
• Severe obesity, as defined by a body mass index of >45.