Chronic fatigue syndrome, also known as CFS or myalgic encephalomyelitis, is a disorder which is not well understood. Symptoms of chronic fatigue syndrome, which include fatigue and joint and muscle pain, seem to appear without cause or any apparent trigger. While there are some strong theories which suggest a particular cause for the disorder, there are still no clear answers.
There are some signs and symptoms of chronic fatigue syndrome which are constant in virtually all cases. The classic sign is simply fatigue, but fatigue on its own does not necessarily indicate CFS. For diagnostic purposes, the fatigue must have been present for at least six months prior to diagnosis. In addition, there must be no other cause that may explain the presence of fatigue. For some people, the fatigue may follow a viral infection, but prior viral infection is not present in all cases.
The fatigue experienced with CFS has other common characteristics. One of these is post-exertional fatigue, which means people with CFS are exhausted after activities they would have not been fatigued by prior to CFS development. Another characteristic is that people with CFS are not refreshed by sleep or rest. Other common symptoms of chronic fatigue syndrome include muscle and joint pain, headaches, fever, and sore throat.
People with CFS may also suffer from neurological problems. One of these is a cognitive disorder called dysnomia. People with this disorder have trouble with speech, and have problems thinking of the right words to use when speaking. Memory dysfunction is also common; however only short-term memory tends to suffer, while long-term memory is retained. Depression is another neurological symptom which may result from CFS, but the disorder does not cause the depression. Instead, the depression tends to develop as a result of the problems that people with CFS face in everyday life.
Because the cause of the disorder is unknown, the question of what causes symptoms of chronic fatigue syndrome is equally difficult to answer. One of the strongest theories on the cause of CFS is that of central sensitization, which describes a particular type of abnormal immune reaction. When the body is in a state of central sensitization, the result is a chronically active immune system. In effect, the immune system behaves as though it is constantly fighting infection. This may explain, in part, why intense fatigue is one of the hallmark symptoms of chronic fatigue syndrome, as the body can expend a large amount of energy when fighting infection.