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  • Updated 12.12.2023
  • Released 05.13.1996
  • Expires For CME 12.12.2026

Chronic fatigue syndrome



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 treatment method, and even the nomenclature vary 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 because reliable diagnostic tests and biological markers remain elusive despite several consensus criteria available (ie, Canadian Consensus Criteria, Fukuda, Oxford, International Criteria, etc.). 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 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 approximately 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 (43). During this time, psychiatry became more sophisticated, and neurasthenia was seen as a psychiatric rather than a neurologic condition (28).

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 (“Royal Free disease”). 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 (proposed by the European psychiatric society in 1970) and neuromyasthenia developed as a result of the transmissible hypothesis, though many suggested mass hysteria was the true origin.

In 1986, Ramsay published the first diagnostic criteria for myalgic encephalomyelitis, a condition characterized by a unique and chronic form of muscle fatigability after even a minor degree of physical effort.

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. The CDC recognized that myalgic encephalomyelitis was the most accepted name in other parts of the world. This was the origin of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), the term for this condition now accepted worldwide (15). 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 (22).

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