Chronic fatigue syndrome.

The chronic fatigue syndrome is an illness of unknown etiology characterized by severe fatigue, myalgias, lymphadenopathy, arthralgias, chills, fevers, and postexertional malaise. Recognizing chronic fatigue syndrome is primarily a method of exclusion with no definitive diagnostic test or physical findings. As research continues to delve into the many possible etiologic agents for chronic fatigue syndrome--infectious, immunologic, neurologic, or psychiatric alone or in combination--the answer remains elusive. What is known is that chronic fatigue syndrome is a heterogeneous disorder very possibly involving an interaction of biological systems. Therefore, chronic fatigue syndrome may describe a large subset of patients, each exhibiting unique symptoms and serologic profiles dependent on the nature of the onset of illness and the genetic profile of individual patients.