Chronic fatigue syndrome (CFS), also referred to as myalgic encephalomyelitis (ME) and often called the "invisible disease", is defined as chronic fatigue that lasts at least six months and cannot be explained by any other illness. It is characterized by a symptom cluster presenting as pathological fatigue and malaise that is worse after exertion, cognitive and immune dysfunctions, muscle pain, lymphadenopathy and sleep disturbances. It usually begins abruptly with a range of flu-like symptoms including muscle fatigue, fevers, lymph-node swelling, persistent diarrhoea, joint and body pain, digestive problems, inability to think, loss of short-term memory and depression. The controversial and mysterious ailment has gone by various names for more than a century. Most doctors recognize the condition, others are skeptical about its existence, wondering if such fatigue is psychologically perpetuated.
Because some people develop chronic fatigue syndrome after having a viral infection, researchers question whether some viruses might trigger the disorder. Suspicious viruses include Epstein-Barr virus, human herpes virus 6, mouse leukemia viruses and Covid-SARs2 virus.
Researchers are testing two other hypotheses. One involves previous findings that patients with CFS who have no psychiatric problems have abnormalities in the structure of their brains; the other concerns preliminary data that CFS patients have something wrong with their hearts or blood vessels. Still other doctors of naturopathic practice argue that this syndrome, or clinical picture, is symptomic of a combination of fatigue (poor cellular energy delivery) and inflammation.
Much of the history of CFS revolves around the efforts to define it and the debates over what to call it. Other diseases that started out being called by one name were later renamed, either for the sake of medical accuracy or for political correctness, which has made it difficult to pinpoint exactly when and where this disease came from. Although the characteristic symptoms of CFS were first described in 1750, the disease has gone through many different names and was first publicly defined as Chronic Fatigue Syndrome in 1988.
In 1992, researchers reported evidence of inflammation in the brains of patients. Imaging scans showed pinpoint areas of swelling or loss of part of the sheath that surround nerve cells in the central nervous system scattered throughout the brain in 113 of 144 patients (78%). The abnormal areas were detected on repeat imaging and in some cases even after symptoms had eased. They are believed to be associated with a virus, but the identity is yet unconfirmed; herpes virus 6 (HHV-6) is suspected. The syndrome may in some unknown way lead to an abnormality of the immune system, which in turn reactivates a virus that has long been dormant in the body (HHV-6 infects virtually everybody in the first years of life).
A 1993 report found that chronic fatigue sufferers tend to breathe from their upper bodies, rather than from their abdomens, which results in irregular breathing and heart rate patterns. Some physicians suggested the bodies of those affected by chronic fatigue conserve energy in different ways than those of non-sufferers.
A 1995 study showed that 70% of patients had a brain stem abnormality that reduced blood flow. In other patients, not enough of the brain steroidal hormone, cortisol, was produced, and moreover the hormone did not function properly, preventing the brain from reacting to stress.
In 1995, chronic fatigue syndrome was tentatively linked to abnormalities in the regulation of blood pressure, namely neurally mediated hypotension, vasovagal syncope, vasodepressor syncope and neurocardiogenic syncope. A virus infection is a probable trigger, since not all people with abnormal blood pressure regulation develop the syndrome. An additional factor is the salt level in the diet; people who eat a lot of salt do not have the syndrome.
Chronic fatigue syndrome (CFS) has remained a medical enigma since it was first reported in the late 1980s by Paul Cheney, MD, PhD, who—along with his medical partner in Incline Village, Nevada—made the observation of a group of his patients all having serious and unremitting fatigue following a significant winter flu season.
ME/CFS may begin as early as age 10 and as late as age 77. It is estimated that between 1 and 2.5 million people in the United States have this condition, resulting in an annual treatment cost of $17 to $24 billion dollars; estimates vary from 17 – 24 million people with ME/CFS worldwide. Although research has shown that ME/CFS is about two to four times more likely to occur in women than men, ME/CFS strikes people from every age, racial, ethnic, and socioeconomic group. Some studies show that ME/CFS may be more common in minority groups.
CFS is a multi-system illness, with many patients experiencing unbalanced gut microbiota. In these patients, alterations in the gut microbiota may contribute to the development of symptoms such as depression, neurocognitive impairments (affecting memory, thought and communication), pain and sleep disturbance.