Centers for Disease Control and Prevention Case Definition of Chronic Fatigue Syndrome*

CFS is a syndrome characterized by fatigue that is:

• Medically unexplained
• Of new onset
• Of at least six months' duration
• Not the result of ongoing exertion
• Not substantially relieved by rest
• Causes a substantial reduction in previous levels of occupational, educational, social or personal activities

In addition, there must be four or more of the following symptoms:

• Impaired memory or concentration
• Sore throat
• Tender neck (cervical) or armpit (axillary) lymph nodes
• Muscle pain (myalgia)
• Headaches of a new type, pattern or severity
• Unrefreshing sleep
• Post-exertiional malaise (lasting more than 24 hours)
• Multi-joint pain (arthralgia without swelling or redness)

Conditions that would exclude a diagnosis of CFS include other medical disorders known to cause fatigue, major depressive illness, medication that causes fatigue as a side effect, and alcohol or substance abuse.

*Fukuda et al, The chronic fatigue syndrome: a comprehensive approach to its definition and study, Ann Intern Med., 1994; 121:953-59.