Chronic fatigue syndrome

William L Conte MD (

Dr. Conte of The University of Chicago received honorariums from Sanofi Genzyme and Genentech for serving as a consultant.

Anthony T Reder MD, editor. (

Dr. Reder of the University of Chicago received honorariums from Bayer, Biogen Idec, Caremark Rx, Genentech, Genzyme, Novartis, Mallinckrodt, Mylan, Serono, and Teva-Marion for service on advisory boards and as a consultant as well as stock options from NKMax America for advisory work.

Originally released May 13, 1996; last updated January 9, 2020; expires January 9, 2023

This article includes discussion of chronic fatigue syndrome, postviral chronic fatigue syndrome, chronic mononucleosis syndrome, Tahoe flu, myalgic encephalomyelitis, neurasthenia, chronic fatigue and immune dysfunction syndrome, AIDS minor, yuppie flu, bored housewife syndrome, and effort syndromes. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.


Chronic fatigue syndrome, also known as myalgic encephalomyelitis or chronic fatigue immune dysfunction syndrome, is a debilitating illness diagnosed by means of exclusion. The illness is often controversial; the proposed etiology, preferred method of treatment, and even the nomenclature varies widely from source to source. The symptoms are also diverse and fluctuating, making uniform studies and research difficult. Even diagnosing chronic fatigue syndrome is a challenge as reliable diagnostic tests and biological markers remain elusive. Little is certain about this illness, but this article summarizes most of the current and widely accepted information about the subject.

Historical note and terminology

There is considerable belief that the history of chronic fatigue syndrome, termed myalgic encephalomyelitis in Great Britain, dates back to the 1800s. In 1869, American neurologist George Beard described a disease known as neurasthenia, an organic illness that caused disabling fatigue of the mind and body. Neurasthenia, which included around 70 symptoms, became a popular and often overused diagnosis in the late 1800s, but fell out of favor around 1918 when it became perceived as primarily psychological and was abandoned by neurologists.

By World War I, neurasthenia was rarely diagnosed. The fatigue illnesses affecting World War I soldiers, called effort syndromes, gained national attention, but subsequent studies by distinguished cardiologist Paul Wood concluded that psychological factors were again the primary trigger, and the conditions were placed instead in the realm of psychiatry (Moss-Morris and Petrie 2001). During this time, psychiatry became more sophisticated, and neurasthenia was seen as a psychiatric rather than a neurologic condition (Friedberg and Jason 1998).

Nonetheless, worldwide incidences of fatigue syndromes have been reported in medical publications for centuries. Notable epidemics occurred at the Los Angeles County Hospital in 1934 and at the Royal Free Hospital in London in 1955. The symptoms were primarily neuromuscular (such as muscle weakness, headache, profound fatigue, and confusion), and an infective agent was thought to be rooted in the epidemics. The terms myalgic encephalomyelitis and neuromyasthenia developed as a result of the transmissible hypothesis, though many suggested mass hysteria was the true origin.

The disorder was officially termed “chronic fatigue syndrome” in late 1988 by the Centers for Disease Control. In 1994, the Centers for Disease Control began recognizing a definition of chronic fatigue syndrome based on the research of an international panel of chronic fatigue syndrome investigators. More than 100 years after the proposed neurasthenia diagnosis, medical disagreements returned to the nature of the disorder. Although chronic fatigue syndrome is a clinically defined medical condition, there is a long history of debate regarding its etiology (Englebienne and De Meirleir 2002).

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