Clinical descriptions of chronic fatigue syndrome

The clinical descriptions of chronic fatigue syndrome (CFS) vary. Different agencies and scientific bodies have produced different guidelines to define the condition, with some overlap of symptoms between descriptions. Aspects of the condition are controversial, with disagreements over etiology, pathophysiology, treatment and naming between medical practitioners, researchers, patients and advocacy groups. Subgroup analysis suggests that, depending on the applied definition, the CFS population may represent a variety of conditions rather than a single disease entity.

The most widely used diagnostic criteria for CFS are the 1994 research guidelines proposed by the "International Chronic Fatigue Syndrome Study Group", led by the Centers for Disease Control and Prevention. These criteria are sometimes called the "Fukuda definition" after the first author (Keiji Fukuda) of the publication. The 1994 CDC criteria specify the following conditions must be met:

Clinically evaluated, unexplained, persistent or relapsing chronic fatigue that is:

The concurrent occurrence of four or more of the following symptoms, all of which must have persisted or recurred during six or more consecutive months of illness and must not have predated the fatigue:

All other known causes of chronic fatigue must have been ruled out, specifically clinical depression, side effects of medication, eating disorders and substance abuse.

The clinical evaluation should include:

Other diagnostic tests have no recognized value unless indicated on an individual basis to confirm or exclude a differential diagnosis, such as multiple sclerosis.

The initial chronic fatigue syndrome definition was published in 1988. It is also called the "Holmes definition", after the manuscript's first author. Unlike the 1994 CDC criteria, the Holmes criteria exclude patients with psychiatric diagnoses and require the presence of eight secondary symptoms, not just four.

The Oxford criteria was published in 1991 and include both CFS of unknown etiology and a subtype of CFS called post-infectious fatigue syndrome (PIFS), which "either follows an infection or is associated with a current infection." Important differences are that the presence of mental fatigue is necessary to fulfill the criteria and symptoms are accepted that may suggest a psychiatric disorder.

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