Fatigue is a common complaint experienced by most of subjects during
lifetime, which
affects approximately 30–50% of general population as point prevalence.
1According to the fatigue-lasting duration, it is classified as acute (<1 month), prolonged (>1 month, <6 months), and chronic fatigue (≥6 months), respectively. Acute fatigue is generally disappears after taking a
rest or treating the causative diseases, while uncontrolled prolonged and chronic fatigue limit the physical and social activities.
2 Especially, medically unexplained chronic fatigue is a debilitating status, such as idiopathic chronic fatigue (ICF) and
chronic fatigue syndrome (CFS).
On the other hand, to distinguish CFS from chronic
fatigue or ICF is very important in clinical practice. The reason is that although patients present fatigue
symptom as their main complaint in subjects suffering from chronic fatigue or CFS, CFS is considered as to being in totally different pathologic illness.
3 In 2015, US Institute of Medicine (IOM) reported
diagnostic criteria for CFS as follows; three mandatory symptoms, a substantial impairment in activities accompanied by fatigue persisting for more than 6 months, post-exertional
malaise (PEM) and unrefreshing
sleep, and one optional symptom among
cognitive impairment or orthostatic intolerance.
4Unlike chronic fatigue, CFS has characteristics of
brain and CNS symptom and is counted as a complex, multisystem neuroimmune disease. As commonly referred to
myalgic encephalomyelitis (ME)/CFS together,
brain inflammation is frequently implied in pathology of CFS.
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