Chronic fatigue syndrome can cause symptoms so severe that people cannot function normally. There is no simple test to diagnose the illness, but researchers, including a group at the University of Miami, are working on that and on how best to treat the syndrome.

The U.S. Centers for Disease Control and Prevention says doctors should consider CFS in patients with six months or more of unexplained fatigue accompanied by other characteristic symptoms, including:

• Cognitive dysfunction, including impaired memory or concentration.

• Exhaustion lasting more than 24 hours after physical or mental exercise.

• Unrefreshing sleep, joint pain without redness or swelling, or persistent muscle pain.

• Headaches of a new type or severity.

• Tender lymph nodes or sore throat.

RESOURCESThe CDC has more information at www.cdc.gov/cfs. A local patient group, PANDORA, or Patient Alliance for Neuroendocrine-immune Disorders Organization for Research and Advocacy, has a Web site: www.pandoranet.info.