Chronic fatigue syndrome (CFS) is a condition of excessive fatigue, cognitive impairment and other varied symptoms. Classified by the World Health Organization (WHO) as a disease of the nervous system, it is of unknown etiology and may last months or years, causing severe debility.

In strict medical terms, the name chronic fatigue syndrome refers only to a pattern of symptoms, and may in fact reflect several different disorders causing similar symptoms. While it can certainly be classified as a disease, there are no investigations that can confirm or rule out the diagnosis. Certain scoring systems have been designed to classify symptoms

Many theories have been advanced regarding the origin of Chronic Fatigue Syndrome ranging from a virally triggered immune dysfunction (RNase L deregulation) and/or brain disorder, natural killer cell dysfunction, metabolic dysfunction, a hypercoagulative blood disorder, a hidden thyroid disorder etc. as well as a disease of psychological origin or a combination of the above. Endocrinological tests indicate that it is not allied to depression.

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