Chronic Fatigue Syndrome: The Published Case Definition

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Following is the case definition for Chronic Fatigue Syndrome (CFS) as published in the December 1994 Annals of Internal Medicine. It includes a conceptual design for CFS and a set of research guidelines for use in studying patients with unexplained fatigue. The authors represent the CDC, the NIH, and a broad spectrum of researchers and clinicians working with Chronic Fatigue Syndrome patients.

Case Definition for Chronic Fatigue Syndrome


Patients must have otherwise unexplained, relapsing fatigue that is new (not life-long); not the result of ongoing exertion; not relieved by rest; and that results in substantial decrease in levels of occupational, social, educational, or personal activities.


The patient must have four or more of the following eight symptoms. Symptoms must persist for six months and the patient must not have predated fatigue.

Self-reported impairment of memory or concentration that affects occupational, social, educational, or personal activities.

Sore throat.

Tender cervical (neck area) or axillary (underarm area) nodes.

Myalgias (muscle pain).

Arthralgias (pain along the nerve of a joint). No redness or swelling.

Headache of a new type.

Unrefreshing sleep.

Post-exertional malaise, lasting at least 24 hours.

Clinical and Laboratory Evaluation Should Include:

Thorough medical history.

Mental status examination. Evidence of psychiatric or neurologic disorders requires consultation.

Thorough physical examination.

Tests to rule out other illnesses. Tests should include the following:

Complete blood count.

Erythrocyte sedimentation rate.

Chemistry panel.


Thyroid stimulating hormone.

Further testing may be suggested on an individual basis; for example, an MRI to rule out multiple sclerosis.

The authors stated that conditions which can explain fatigue, in their opinion, rule out the diagnosis of Chronic Fatigue Syndrome. Examples of such conditions include:

A medical condition, such as untreated hypothyroidism, sleep apnea, narcolepsy, or the effects of some medications.

Previously diagnosed and unresolved medical conditions such as malignancy or chronic hepatitis.

Major psychiatric disorders, past or present, including major depressive disorder, bipolar disease, schizophrenia, anorexia nervosa, or bulimia.

Substance abuse within two years before the onset of fatigue or at any time after the onset.

Severe obesity

Conditions that do not explain fatigue, and thus are permitted in the case definition, include:

Conditions that cannot be confirmed by laboratory tests, such as fibromyalgia, anxiety disorders, non-psychotic depression, or multiple chemical sensitivities.

Medical conditions which might cause fatigue but have been treated adequately; for example, hypothyroidism with normal blood thyroid levels.

Lyme disease or syphilis treated before the onset of CFS.

Any isolated or unexplained physical finding or laboratory test.

Idiopathic Chronic Fatigue

This is the new term defined as clinically evaluated chronic fatigue that fails to meet the above criteria. The reasons for failing to meet criteria should be specified.

Excerpted from “Defining Chronic Fatigue Syndrome” by Philip K. Nelson, M.D., The Manasota Palmetto, January 1995, Sarasota, FL. Reprinted with permission.

See related article(s): Coping with CFIDS | Doctors Who Treat CFIDS

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