Many people have disorders for which no specific cause has been identified. Some doctors believe that some of these disorders of unknown cause are due to psychologic factors. Others believe that the disorders are caused by infections (such as viral infections), toxic chemicals, or abnormalities of the immune system. Although a cause has not been proved for any of these disorders, many people undergo considerable testing and try unproved treatments in time-consuming and costly attempts to diagnose and relieve their symptoms. Some people thought to have disorders of unknown cause actually have common disorders that are in the early stages (before the typical symptoms have developed) or that have unusual symptoms.

Last full review/revision December 2008 by Margaret-Mary G. Wilson, MD