Another review found that children have a better prognosis than adults, with 54–94% having recovered by follow-up, compared to less than 10% of adults returning to pre-illness levels of functioning. Epidemiology
The prevalence rates for CFS/ME vary widely depending on "case definitions and diagnostic methods". Based on the 1994 CDC diagnostic criteria, the global prevalence rate for CFS is 0.89%. In comparison, the prevalence rate for the stricter criteria, such as the 1988 CDC "Holmes" criteria for CFS and the 2003 Canadian criteria for ME (both of which, for example, exclude patients with psychiatric diagnoses), produce an incidence rate of only 0.17%. For an example of how these rates impact a nation: the CDC website notes that  between 836,000 and 2.5 million Americans have ME/CFS, "but most remain undiagnosed".Females are diagnosed about 1.5 to 2.0 times more often with CFS than males. An estimated 0.5% of children have CFS, and more adolescents are affected with the illness than younger children. : 182 The incidence rate according to age has two peaks, one at 10–19 and another at 30–39 years. The effect is seen both in female and in male data, but is more pronounce in females. It was suggested that this occurs because these age groups may be more vulnerable to CFS. The rate of prevalence is highest between ages 40 and 60. History
Myalgic encephalomyelitis
From 1934 onwards, outbreaks of a previously unknown illness began to be recorded by doctors. Initially considered to be occurrences of poliomyelitis, the illness was subsequently referred to as "epidemic neuromyasthenia".
Cerebral hypoxia is a form of hypoxia (reduced supply of oxygen), specifically involving the brain; when the brain is completely deprived of oxygen, it is called cerebral anoxia. There are four categories of cerebral hypoxia; they are, in order of increasing severity: diffuse cerebral hypoxia (DCH), focal cerebral ischemia, cerebral infarction, and global cerebral ischemia. Prolonged hypoxia induces neuronal cell death via apoptosis, resulting in a hypoxic brain injury.Cases of total oxygen deprivation are termed "anoxia", which can be hypoxic in origin (reduced oxygen availability) or ischemic in origin (oxygen deprivation due to a disruption in blood flow). Brain injury as a result of oxygen deprivation either due to hypoxic or anoxic mechanisms are generally termed hypoxic/anoxic injuries (HAI). Hypoxic ischemic encephalopathy (HIE) is a condition that occurs when the entire brain is deprived of an adequate oxygen supply, but the deprivation is not total. While HIE is associated in most cases with oxygen deprivation in the neonate due to birth asphyxia, it can occur in all age groups, and is often a complication of cardiac arrest. Signs and symptoms
The brain requires approximately 3.3 ml of oxygen per 100 g of brain tissue per minute. Initially the body responds to lowered blood oxygen by redirecting blood to the brain and increasing cerebral blood flow. Blood flow may increase up to twice the normal flow but no more.