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Chronic fatigue syndrome

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Chronic fatigue syndrome
Classification and external resources
ICD-10 G93.3
ICD-9 780.71
DiseasesDB 1645
MedlinePlus 001244
eMedicine med/3392  ped/2795
MeSH D015673

Chronic fatigue syndrome (CFS) is the most common name given to a poorly understood, variably debilitating disorder or disorders of uncertain causation.

Symptoms of CFS include widespread muscle and joint pain, cognitive difficulties, chronic, often severe mental and physical exhaustion and other characteristic symptoms in a previously healthy and active person. Fatigue is a common symptom in many illnesses, but CFS is a multi-systemic disease and is relatively rare by comparison.[1] Diagnosis requires a number of features, the most common being severe mental and physical exhaustion which is "unrelieved by rest" and is worsened by exertion. Most diagnostic criteria require that symptoms must be present for at least six months, and all state the symptoms must not be caused by other medical conditions. CFS patients may report additional symptoms,[2] including muscle weakness, cognitive dysfunction, hypersensitivity, orthostatic intolerance, digestive disturbances, depression, poor immune response, and cardiac and respiratory problems. It is unclear if these symptoms represent co-morbid conditions or are produced by an underlying etiology of CFS.[3] Full resolution occurs in only 5-10% of cases.[4]

CFS is thought to have an incidence of 4 adults per 1,000 in the United States.[5] For unknown reasons, CFS occurs more often in women than men, and in people in their 40s and 50s.[6][7] The illness is estimated to be less prevalent among children and adolescents, but studies are contradictory as to the degree.[citation needed] There is no medical test which is widely accepted to be diagnostic of CFS. It remains a diagnosis of exclusion based largely on patient history and symptomatic criteria, although a number of tests can aid diagnosis.[8]

Whereas there is agreement on the genuine threat to health, happiness, and productivity posed by CFS, various physicians groups, researchers, and patient activists promote different nomenclature, diagnostic criteria, etiologic hypotheses, and treatments, resulting in controversy about nearly all aspects of the disorder. The name CFS itself is controversial, as advocacy groups as well as some experts feel it trivializes the illness and have supported efforts to change it. The World Health Organization's ICD uses the terms post-viral fatigue syndrome and benign myalgic encephalomyelitis. Another alternative name for CFS is chronic fatigue immune dysfunction syndrome.

Contents

[edit] Signs and symptoms

[edit] Onset

The majority of CFS cases start suddenly,[9] usually accompanied by a "flu-like illness"[3] which is more likely to occur in winter,[10][11] while a significant proportion of cases begin within several months of severe adverse stress.[12][13][9] Because some people have a case of flu-like or other respiratory infection such as bronchitis, from which they seem never to fully recover, an Australian research group states that post-viral fatigue syndrome could be a subset of CFS.[14][not in citation given] The accurate prevalence and exact roles of infection and stress in the development of CFS however are currently unknown.

[edit] Symptoms

The United States Centers for Disease Control (CDC) has established a definition of CFS[15] that is the most commonly used in research and clinical applications.[2] According to the CDC, CFS involves:

1. Fatigue, unexplained, persisting (lasting six months or longer), "not due to ongoing exertion," and not substantially reduced by rest. The person must have experienced a significant reduction in activity levels.
2. Four or more of the following symptoms:
  • Impaired memory or concentration
  • Post-exertional malaise, where physical or mental exertions bring on "extreme, prolonged exhaustion and sickness"
  • Unrefreshing sleep
  • Muscle pain (myalgia)
  • Pain in multiple joints (arthralgia)
  • Headaches of a new kind or greater severity
  • Sore throat, frequent or recurring
  • Tender lymph nodes (cervical or axillary)

When symptoms can be due to other conditions, the diagnosis of CFS is excluded. The CDC specifically refers to several problems with symptoms resembling those of CFS: "mononucleosis, Lyme disease, lupus, multiple sclerosis, fibromyalgia, primary sleep disorders, severe obesity and major depressive disorders. Medications can also cause side effects that mimic the symptoms of CFS."[15]

[edit] Activity levels

Patients report critical reductions in levels of physical activity[16] and are as impaired as persons whose fatigue can be explained by another medical or a psychiatric condition.[17] According to the CDC, studies show that the degree of functional impairment in some CFS patients may be comparable with other chronic medical conditions such as multiple sclerosis, lupus, rheumatoid arthritis, heart disease, end-stage renal failure and chronic obstructive pulmonary disease (COPD). [18][19] The severity of symptoms and disability is the same in both genders,[20] and chronic pain is strongly disabling in CFS patients,[21] but despite a common diagnosis the functional capacity of CFS patients varies greatly.[22] While some patients are able to lead a relatively normal life, others are totally bed-bound and unable to care for themselves. A systematic review found that in a synthesis of studies, 42% of patients were employed, 54% were unemployed, 64% reported CFS-related work limitations, 55% were on disability benefits or temporary sick leave, and 19% worked full-time.[8]

[edit] Mechanism

Main article: Pathophysiology of chronic fatigue syndrome

The mechanisms and processes (pathogenesis) of chronic fatigue syndrome are unknown,[4] but are the subjects of many research studies, including physiological and epidemiological studies. Hypotheses being researched include viral infection, hypothalamic-pituitary-adrenal axis abnormalities (though it is unclear if this is a cause, or consequence, of CFS), immune dysfunction, mental and psychosocial factors causing or contributing towards CFS.[23] Because of social prejudices assuming that psychological disorders are not biological or "real", many patients object to the idea that the CFS is a mental disorder.[24] Other hypotheses include oxidative stress and genetic predisposition.[25] Both "neuroticism and introversion" may predispose people to getting CFS.[26]

Some researchers say that exposure to chemicals, infectious agents, stress, and other insults in early life may be a component of later-life CFS.[27] Another idea is that a virus or another infectious agent might provoke an abnormal immune response in some people that does not get switched off and becomes chronic.[28]

The central nervous system is important in CFS. Research has been reported on a "Hyperserotonergic state and hypoactivity of the hypothalamic-pituitary-adrenal axis (HPA axis)" in CFS.[29] Genetic factors may be the basis for some of these changes. A 2008 study of gene polymorphisms indicates genetic predisposition possibly resulting in enhanced activity of serotonin.[30] Another report says that low cortisol levels can be responsible: "hypocortisolaemia might sensitize the hypothalamic-pituitary-adrenal axis to development of persistent central fatigue after stress."[31] Some researchers conclude that the involvement of the nervous and immune systems involvements are intertwined.[32]

CFS may be perpetuated when patients fixate on a physical cause of illness and on sensations, and when they implement avoidance behaviors. Lack of support or reinforcement of illness behavior from social networks can also delay recovery, as can conflict with doctors who insist on psychological causes over a patient's objections.[26]

[edit] Classification

Main article: Clinical descriptions of chronic fatigue syndrome

There are no diagnostic tests or physical signs for CFS,[4] so testing is used to rule out other potential causes for symptoms.[33] The most widely used[2] clinical and research description of CFS is the CDC definition published in 1994 (details given above).[33] The 1994 CDC definition, also called the Fukuda definition after the first author on the report, was based on the Holmes or CDC 1988 scoring system.[34] The 1994 criteria require the presence of only four symptoms beyond fatigue, where the 1988 criteria require six to eight.[35]

Other notable definitions include

  • The Oxford criteria (1991)[36]
  • The 2003 Canadian case definition for ME/CFS[37] was developed "in an attempt to exclude psychiatric cases."[26] This definition requires presence of symptoms from at least one category of autonomic, neuroendocrine, or immune symptoms. Doctors with the National Health Service in the UK are discouraged from using this case definition, since requiring the presence of these signs could exclude patients,[35] and the criteria "have not been evaluated for research purposes."[38]

Using different case definitions may influence the types of patients selected.[39] Some authors suggest that subtypes of patients may exist.[40] Clinical practice guidelines, with the aim of improving diagnosis, management, and treatment, are generally based on case descriptions. Guidelines are usually produced at national or international levels by medical associations or governmental bodies after evidence is examined and usually include summarized consensus statements. An example of a CFS guideline for the National Health Service in England and Wales, produced in 2007 by the National Institute for Health and Clinical Excellence (NICE).[35]

[edit] Treatment

Main article: Chronic fatigue syndrome treatment

Many patients do not fully recover from CFS, even with treatment.[41] Some management strategies are suggested to reduce the consequences of having CFS. Medications, other medical treatments, and complementary and alternative medicine are considered, but currently the only known treatments with "scientifically proven value in randomized controlled trials"[2] are the behavioral therapies cognitive behavioral therapy (CBT) and graded exercise therapy (GET). A systematic review published in 2006 in the Journal of the Royal Society of Medicine[42] and a 2006 review in The Lancet found that CBT and GET were the only two known "interventions found to be beneficial,"[26] confirming earlier conclusions.[43][44][45]

[edit] Psychological therapy

The currently most effective known management strategy for CFS is cognitive behavioral therapy (CBT), a form of psychological therapy. Since the cause or causes of CFS are not known, CBT tries to help patients understand their individual symptoms and beliefs and develop strategies to improve day-to-day functioning. CBT has special value for treating medically unexplained symptoms (MUS) like CFS according to Deary et al. who write, "a broadly conceptualized cognitive behavioural model of MUS suggests a novel and plausible mechanism of symptom generation and has heuristic value."[46]

A Cochrane Review meta-analysis of 15 randomized, controlled cognitive behavioral therapy trials with 1043 participants concluded that CBT was an effective treatment. Comparing CBT with "usual care," four reviewed studies showed that CBT was more effective (40% vs 26%). In three studies, CBT worked better than other types of psychological therapies (48% vs 27%). The effects may diminish after therapy is discontinued; the reviewers write that "the evidence base at follow-up is limited to a small group of studies with inconsistent findings" and encourage further studies.[47]

Different trials of CBT use different measures of outcome, and some studies report higher success rates (as high as 70%[48] and 73%[49]) than those reviewed by Cochrane. One study suggests that CBT could facilitate full recovery in some patients, with 69% of the treated patients no longer meeting the CDC criteria for CFS.[50] In a review in The Lancet, Dutch researchers state that while CBT is not necessarily a cure for CFS, in some studies it results in improvements in about 70% of patients. They stress that, with the current understanding of the biological nature of the brain, a psychological CFS model does not preclude neurobiological components.[26]

If CBT works for individual patients depends on many factors. A treatment can only work if patients agree to it, and Cochrane observes an "ambivalence of many CFS patients towards a psychological treatment for symptoms that are experienced as physical."[47] Patient characteristics predicting a poor outcome of CBT include "membership of a self-help group, receipt of a sickness benefit, low sense of control, a strong focus on symptoms, and a pervasively passive activity pattern."[26]

[edit] Exercise therapy

Over half of CFS patients studied experience improvements when using graded exercise therapy (GET), a form of physical therapy.[26] Meta-analysis of multiple randomized, controlled trials of exercise therapy of patients diagnosed with CFS shows improvements in fatigue symptoms over controls.[51][42][52] Some patient organizations dispute the results of the exercise therapy trials.[53]

[edit] Other

Other treatments of CFS have been proposed but not much is known about how effective they are.[26] Medications thought to have promise in alleviating stress-related disorders include antidepressant and immunomodulatory agents such as staphypan Berna, lactic acid bacteria, kuibitang and intravenous immunoglobulin.[54] CFS patients are less susceptible to placebo effects than predicted, and have a low placebo response compared to patients with other diseases.[55] CFS is associated with chemical sensitivity,[56][57] and some patients often respond to a fraction of a therapeutic dose that is normal for other conditions.[58][59] Adaptive pacing is another proposed therapy.[53]

[edit] Prognosis

[edit] Recovery

A systematic review of 14 studies of the outcome of untreated people with CFS found that "the median full recovery rate was 5% (range 0–31%) and the median proportion of patients who improved during follow-up was 39.5% (range 8–63%). Return to work at follow-up ranged from 8 to 30% in the three studies that considered this outcome." .... "In five studies, a worsening of symptoms during the period of follow-up was reported in between 5 and 20% of patients."[60] According to the CDC, delays in diagnosis and treatment can reduce the chance of improvement.[61]

[edit] Deaths

CFS is unlikely to increase the risk of an early death. A systematic review of 14 studies of the outcome of CFS reported 8 deaths, but none were considered directly attributable to CFS.[60] To date there have been two studies directly addressing life expectancy in CFS. In a preliminary 2006 study of CFS self-help group members, it was reported that CFS patients were likely to die at a younger than average age for cancer, heart failure, and suicide.[62] However, a much larger study of 641 CDC criteria diagnosed patients with CFS, who were followed up for a mean of 9 years, showed no excess risk of dying from any cause.[63] A notable death of a CFS patient was Sophia Mirza.[64]

[edit] Epidemiology

Due to problems with the definition of CFS, estimates of its prevalence vary widely. Studies in the United States have previously found between 75 and 420 cases of CFS for every 100,000 adults. The CDC states that more than 1 million Americans have CFS and approximately 80% of the cases are undiagnosed.[4] All ethnic and racial groups appear susceptible to the illness, and lower income groups are slightly more likely to develop CFS.[7] More women than men get CFS — between 60 and 85% of cases are women; however, there is some indication that the prevalence among men is underreported. The illness is reported to occur more frequently in people between the ages of 40 and 59. Blood relatives of people who have CFS appear to be more predisposed.[7][65] However, there is no evidence that CFS is contagious.[66] Caretakers, partners and others in close contact with persons with CFS for years do not develop CFS any more frequently (excluding blood relatives, as earlier).

[edit] Disease associations

Some diseases show a considerable overlap with CFS. Thyroid disorders, anemia, and diabetes are a few of the diseases that must be ruled out if the patient presents with appropriate symptoms.[33][35][67]

People with fibromyalgia (FM, or fibromyalgia syndrome, FMS) have muscle pain and sleep disturbances. Fatigue and muscle pain occurs frequently in the initial phase of various hereditary muscle disorders and in several autoimmune, endocrine and metabolic syndromes; and are frequently labelled as CFS or fibromyalgia in the absence of obvious biochemical/metabolic abnormalities and neurological symptoms.[citation needed] Those with multiple chemical sensitivity (MCS) are sensitive to chemicals and have sleep disturbances. Many veterans with Gulf War syndrome (GWS) have symptoms almost identical to CFS.[68] One study found several parallels when relating the symptoms of Post-polio syndrome with CFS, and postulates a possible common pathophysiology for the illnesses.[69]

Although post-Lyme syndrome and CFS share many features/symptoms, a study found that patients of the former experience more cognitive impairment and the patients of the latter experience more flu-like symptoms.[70]

One review (2006) found that there was a lack of literature to establish the discriminant validity of undifferentiated somatoform disorder from CFS. The author stated that there is a need for proponents of chronic fatigue syndrome to distinguish it from undifferentiated somatoform disorder. The author also mentioned that the experience of fatigue as exclusively physical and not mental is captured by the definition of somatoform disorder but not CFS.[71] Hysterical diagnoses are not merely diagnoses of exclusion but require criteria to be met on the positive grounds of both primary and secondary gain.[72] Primary depression can be excluded in the differential diagnosis due to the absence of anhedonia and la belle indifference, the variability (lability) of mood, and the presence of sensory phenomena and somatic signs such as ataxia, myclonus and most importantly, exercise intolerance with paresis, malaise and general deterioration.[citation needed] Feeling depressed is also a commonplace reaction to the losses caused by chronic illness[73] which can in some cases become a comorbid situational depression.

[edit] Co-morbidity

Many CFS patients will also have, or appear to have, other medical problems or related diagnoses. Co-morbid fibromyalgia is common, where only patients with fibromyalgia show abnormal pain responses.[74] Fibromyalgia occurs in a large percentage of CFS patients between onset and the second year, and some researchers suggest fibromyalgia and CFS are related.[75] Similarly, multiple chemical sensitivity (MCS) is reported by many CFS patients, and it is speculated that these similar conditions may be related by some underlying mechanism, such as elevated nitric oxide/peroxynitrite.[76] As previously mentioned, many CFS sufferers also experience symptoms of irritable bowel syndrome, temporomandibular joint pain, headache including migraines, and other forms of myalgia. Clinical depression and anxiety are also commonly co-morbid. Compared with the non-fatigued population, male CFS patients are more likely to experience chronic pelvic pain syndrome (CP/CPPS), and female CFS patients are also more likely to experience chronic pelvic pain.[77] CFS is significantly more common in women with endometriosis compared with women in the general USA population.[78]

[edit] History

Main article: History of chronic fatigue syndrome

A major outbreak of a condition similar to CFS in 1934 at the Los Angeles County Hospital affected all or most of its nurses and doctors. It was referred to as Atypical Poliomyelitis, and was generally believed to be a form of polio.[79]

The outbreak that gave rise to the name Royal Free Disease or Benign Myalgic Encephalomyelitis (see History of chronic fatigue syndrome) occurred at London's Royal Free Hospital in 1955, affecting mostly the hospital staff, and formed the basis of descriptions by Achenson, Ramsay, and others.[80]

(Benign) Myalgic Encephalomyelitis was first classified into the International Classification of Diseases in 1969 under Diseases of the nervous system.[81]

The name chronic fatigue syndrome has been attributed to the 1988 article, "Chronic fatigue syndrome: a working case definition", (the Holmes definition). This research case definition was published after US Centers for Disease Control epidemiologists examined patients at the Lake Tahoe outbreak.[82][83][34]

In 2006 the CDC estimated there were more than 1 million cases of CFS in the US and commenced a public awareness program.[4]

[edit] Society and culture

[edit] Social issues

Many patients report that a chronic fatigue syndrome diagnosis carries a considerable stigma, and has frequently been viewed as malingering, hypochondria, phobia, "wanting attention" or "yuppie flu". As there is no objective test for the condition at this time, it has been argued that it is easy to invent or feign CFS-like symptoms for financial, social, or emotional benefits.[84][85] CFS sufferers argue in turn that the perceived "benefits" are hardly as generous as some may believe, and that CFS patients would greatly prefer to be healthy and independent. A study found that CFS patients endure a heavy psychosocial burden.[86] 2,338 respondents of a survey by a UK patient organization highlights that those with the worst symptoms often receive the least support from health and social services.[87] A study found that CFS patients receive worse social support than disease-free cancer patients or healthy controls, which may perpetuate fatigue severity and functional impairment in CFS.[88] A survey by the Thymes Trust found that children with CFS often state that they struggle for recognition of their needs and/or they feel bullied by medical and educational professionals.[89] The ambiguity of the status of CFS as a medical condition may cause higher perceived stigma.[90] A study suggests that while there are no gender differences in CFS symptoms, men and women have different perceptions of their illness and are treated differently by the medical profession.[91] Anxiety and depression often result from the emotional, social and financial crises caused by CFS. While few studies have been made, it is believed that CFS patients are at a high risk of suicide.[92]

[edit] Doctor-patient relations

Some in the medical community did not at first recognize CFS as a real condition, nor was there agreement on its prevalence.[93][94] There has been much disagreement over proposed causes, diagnosis, and treatment of the illness.[95][96][97][98][99] The context of contested causation may affect the lives of the individuals diagnosed with CFS, affecting the patient-doctor relationship, the doctor's confidence in their ability to diagnose and treat, ability to share issues and control in diagnosis with the patient, and raise problematic issues of reparation, compensation, and blame.[100] The etiology is unknown and a major divide exists over whether funding for research and treatment should focus on physiological, psychological or psychosocial aspects of CFS. The division is especially great between patient groups and psychological and psychosocial treatment advocates in Great Britain.[99] Sufferers describe the struggle for healthcare and legitimacy due to bureaucratic denial of the condition because of its lack of a known etiology. Disagreements over how the condition is dealt with by health care systems has resulted in an expensive and prolonged conflict for all involved.[101][94]

[edit] Nomenclature

Main article: Alternative names for chronic fatigue syndrome

The nomenclature of the condition(s) has been challenging, since consensus is lacking within the clinical, research, and patient communities regarding its defining features and causes. Authorities on the illness look upon the condition as a central nervous system, metabolic, (post-)infectious, cardiovascular, immune system or psychiatric disorder, and consider the possibility that it is not a single homogenous disorder (with a range of possible clinical presentations), but a group of several distinct disorders with many clinical characteristics in common.

Over time and in different countries many names have been associated with the condition(s). Aside from CFS, some other names used include Akureyri disease, benign myalgic encephalomyelitis, chronic fatigue immune dysfunction syndrome, chronic infectious mononucleosis, epidemic myalgic encephalomyelitis, epidemic neuromyasthenia, Iceland disease, myalgic encephalomyelitis (ME, particularly in the United Kingdom, Canada, New Zealand and Australia), myalgic encephalitis, myalgic encephalopathy, post-viral fatigue syndrome, raphe nucleus encephalopathy, Royal Free disease, Tapanui flu and yuppie flu (now considered pejorative).[102][103] Many patients particularly prefer what they feel is a more "medical-sounding" term, such as "chronic fatigue immune dysfunction syndrome" (CFIDS)[104] or "myalgic encephalomyelitis" (ME), believing the name "chronic fatigue syndrome" trivializes the condition and prevents it from being seen as a serious health problem.[105][106]

Researchers question the accuracy of the term "myalgic encephalomyelitis" since there is "no recognized pathology in muscles and in the central nervous system."[107][108] For this reason, in 1999 the Royal Colleges of Physicians, Psychiatrists, and General Practitioners in the United Kingdom called for doctors to stop using the diagnosis.[107] The Royal Colleges later bowed to protests by patient groups and endorsed using ME along with CFS.[109] A recent review states an article from 1959 suggests ME could be a distinct condition, a current view of some patient groups, but CFS and ME are usually used as synonyms.[44]

[edit] References

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