| Chronic fatigue syndrome is a condition marked by severe chronic mental and physical exhaustion, that is not relieved by rest and is not directly caused by other conditions. To be diagnosed with chronic fatigue syndrome, the tiredness must be severe enough to decrease ability to participate in ordinary activities by 50%. |
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| Despite promising avenues of research, there remains no objective assay or pathological finding which is widely accepted to be diagnostic of CFS, and it remains a diagnosis of exclusion, made on the basis of patient history and symptomatic criteria. |
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