Introduction

Chronic fatigue syndrome (CFS), also sometimes called immune dysfunction syndrome or myalgic encephalomyelitis (in Europe), is not a new disorder. In the 19th century the term neurasthenia, or nervous exhaustion, was applied to symptoms resembling CFS. In the 1930s through the 1950s, outbreaks of disease marked by prolonged fatigue were reported in the United States and many other countries. Beginning in the early to mid-1980s, interest in chronic fatigue syndrome was revived by reports in America and other countries of various outbreaks of long-term debilitating fatigue.

Fatigue that lasts for more than six months, impairs normal activities, and has no identifiable medical or psychological problems to account for it is referred to as unexplained chronic fatigue. These symptoms can be further categorized as follows:

• Chronic fatigue syndrome (CFS). A number of criteria must be met in order for a patient's symptoms to be described as CFS. Six million patient visits are made each year because of fatigue, although only a very small percentage of these can be attributed to actual chronic fatigue syndrome.
• Idiopathic chronic fatigue. If the patient's symptoms do not meet the criteria for CFS, then the condition is referred to as idiopathic chronic fatigue. (Idiopathic simply means that the cause is unknown.)

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Review Date: 1/18/2006
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital