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What is Chronic Fatigue Syndrome (or CFIDS)? 

 There are many different opinions about how to define chronic fatigue syndrome (CFS).   The name “fatigue syndrome” may be misleading.  After all, fatigue is such a common experience, that everyone may well be "chronically fatigued".   The name certainly sounds like harmless and ubiquitous symptom.    Yet, CFS has unique symptoms.   The more distinct clinical symptoms of CFS can be summed up as: 

1.     Prolonged and Disabling Fatigue, Especially Following Exertion/Activity  - This post-exertional fatigue is the hallmark symptom of CFS.   Small tasks, tasks once taken for granted, can cause exacerbation of symptoms for days or even weeks.   Since the price for activity is often incurred after the activity/event, many people with CFS have a difficult time avoiding relapses.  Most people with CFS must slowly learn to manage their activity.  Some people may be bedridden. 


Exercise and activity may temporarily worsen the symptoms of CFS.   These symptoms are:

a.      Flu-like symptoms - Swollen lymph nodes and flu-like muscle aches are common in CFS. Many people with CFS report that their illness began with an acute viral infection.    


b.      Orthostatic Intolerance -  Sitting or standing is something most people take for granted.   For many people who suffer from CFS, remaining stationary and upright can be very uncomfortable.   After sitting or standing, pain in the legs and diminished mental clarity are common.   Many theories abound as to what causes orthostatic intolerance -- inability to sit or stand for prolonged periods -- in people with CFS.  Neurological dysfunction, cardiomyopathy, and hypovolemia (low blood volume) have been suggested as possible culprits.


c.   Neurological Dysfunction - Neurological symptoms will vary greatly from person to person, which is one reason why individual neurological symptoms may not be as accurate in defining CFS.   Some of the more prominent neurological symptoms are diminished mental clarity, extreme mental fatigue, insomnia, and chronic migraines.  Digestive problems and tachycardia (rapid heart rate, especially upon sitting or standing) are also common.


What is the Center Disease for Control's 1994 CFS case definition?

The most widely used definition for CFS is 1994 CDC CFS case definition, also known as the Fukada definition.  The definition is more complex, focusing on eight symptoms.   According to the authors, the goal of the revision was to integrate many fatiguing illnesses under a "fatigue syndrome", enabling CFS research to branch out into other areas, such as fibromyalgia and pain.    The authors of the definition claimed that most fatiguing illnesses were related, and thus, should be studied together with less distinctions made between them.  

        Estimates of CFS jumped after the revision from about 150,000 people in the US under the 1988 definition, to about 1 million.   Many clinicians believe the definition failed by integrating non-similar conditions together in one rubric.  Despite the criticisms, the definition is widely used, perhaps by default. 

What is the 2005 Center for Disease Controls' Revised "Empirical" Definition?

 The CFS research definition was once again broadened  in 2005 by the CDC.  The new research definition focused on chronic unwellness, rather than fatigue or any one symptom.   Once again, estimates of CFS ballooned under the broader definition, and were re-estimated between 4 and 12 million.   CDC researchers who developed the new definition stated that a goal of the broader definition was to increase international attention on CFS and general fatigue, and asserted that reliability would increase by including different fatiguing conditions in research samples.     This definition failed to earn much respect, and even the CDC seemed reluctant to use the new definition.

Where did the terms CFIDS and Myalgic Encephalitis originate?

CFIDS stands for “chronic fatigue and immune dysfunction syndrome”.    The largest advocacy group in the United States, The CFIDS Association of America, has used this name.   Many people with CFS feel that the name “Chronic Fatigue Syndrome” severely trivializes the illness and is such a common symptom that it would lead to a broadening of the illness, over time.  This view led to the eventual merging of the phrase ”immune dysfunction” into the name, yielding the frequently utilized acronym, CFIDS.   The popularity of the term CFIDS may also be attributed to the fact that many cases of CFS are precipitated by a virus.    Subgroups of people with CFS also have been found to have Rnase dysfunction (a viral pathway), high viral titers, white blood cell abnormalities, and circulating cytokines, creating some justification for the name.  

The name M.E.,or Myalgic Encephalomyelitis, is commonly used in the United Kingdom and Australia.   This name is used widely in the U.S as well.   The name also has some historical basis, as it was first used to describe an outbreak of a post-viral illness in the UK in the 1950s.   M.E. is associated with very distinct definition of the illness that emphasizes post-exertional fatigue, rapid onset, and orthostatic intolerance.  Many people feel the M.E. definition is more reliable, especially for research purposes.