Diagnosis

It is very difficult to diagnose chronic fatigue syndrome. Even experts do not have a clear definition of what chronic fatigue actually is, or what mechanisms in the brain or nervous system are responsible for it. The best diagnostic approach is to determine whether the patient matches the criteria for CFS and to rule out other possible causes of symptoms.

Criteria for Chronic Fatigue Syndrome

In May 2006, the Centers for Disease Control and Prevention (CDC) released a revised definition for Chronic Fatigue Syndrome based on a consensus of many of the leading CFS researchers and doctors (including input from patient group representatives). In the revised definition, chronic fatigue syndrome is considered a subset of chronic fatigue, a broader category defined as unexplained fatigue that lasts for 6 months or longer. Chronic fatigue is considered a subset of prolonged fatigue, which is defined as fatigue that lasts for 1 month or more.

Unexplained chronic fatigue can be classified as CFS if the patient meets the following criteria:

1. Unexplained persistent or relapsing chronic fatigue that is either new or that started at a definite period of time; is not the result of ongoing exertion; is not substantially relieved by rest; and significantly reduces activities such as work, education, and social life.
2. Also, four or more of the following symptoms, which must have continued or recurred during 6 or more consecutive months of illness and must not have started before the fatigue:
   • Significant impairment in short-term memory or concentration
   • Sore throat
   • Tender lymph nodes
   • Muscle pain
   • Joint pain without swelling or redness
   • Headaches of a new type, pattern, or severity
   • Unrefreshing sleep
   • Malaise that lasts for more than 24 hours after exertion

Conditions that Can Rule Out a CFS Diagnosis

1. Any active medical condition that may explain the presence of chronic fatigue, such as:
   • Untreated hypothyroidism (underactive thyroid gland)
   • Sleep apnea and narcolepsy (common sleep disorders)
   • Side effects of medication
2. An illness (such as cancer, or hepatitis B or C virus infection) that relapsed or did not completely get better during treatment, that could explain the presence of chronic fatigue.
3. A past or current major depressive disorder, such as:
   • Bipolar affective disorder
   • Schizophrenia
   • Delusional disorder
   • Dementia
   • Anorexia nervosa or bulimia nervosa
4. Alcohol or other substance abuse that occurs within 2 years of the onset of chronic fatigue and at any time afterward.
5. Severe obesity, as defined by a body mass index (BMI) equal to or greater than 45. (Note: Body mass index values vary considerably among different age groups and populations. No "normal" or "average" range of values can be suggested. The range of 45 BMI or higher was selected because it falls within the range of severe obesity.)

Any other abnormality found during an exam or other tests that could explain CFS symptoms must be resolved before further attempting to classify the condition.