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What are CFS, ME, and FMS?

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Chronic Fatigue Syndrome (CFS/CFIDS) & Fibromyalgia (FM)
are terms used in the United States.
Myalgic Encephalopathy/Encephalomyelitis (ME/M.E.) is used internationally.

What is CFS?
Official CFS/ME Case Definitions & History
CFS Prevalence

What is FMS?
Official FM Case Definitions
FM Prevalence

Common Acronyms

There is controversy in defining syndromes, determining who in particular has them,
and deciphering how many in the general population have them.
There is intrigue behind some of the information sources.

Some of the many mixed messages involved in CFS/FM:

CFS and FM are the same/different
CFS or FM is rare/quite prevalent
Only a few/many experience recovery
Its only physical / its only the other / it is that body-mind split

"There are political, medical, funding, and other reasons for considering CFS and FM differently, but I suggest staying aware of what goes on in both worlds. There is so much overlap in coping, treatment, and description, I prefer to welcome people with either or both or similar conditions to our support group.  While the headlining symptoms of CFS and FM are experientially very different -- it feels different to be in pain than it does to be exhausted in the extreme, than it does to feel both, -- we have much to offer and learn from one another. Mixed messages ultimately prod us to dig deeper,
to figure out what fits best for us as individuals."
- Elly Brosius

Please also see our page about the syndrome of Orthostatic Intolerance (OI).
It may be overlapping and aggravating your CFS and/or FM.
Learning about OI gives more practical treatments to help yourself.

What is CFS?

ME/CFS Primer for Clinical Practitioners
 IACFS/ME - 5-5-12
The goal of the Primer is to provide the information necessary for clinicians to understand, diagnose, and manage the symptoms of ME/CFS.

International Consensus Criteria Published for Myalgic Encephalomyelitis
 Research1st by K. Kimberly McCleary - 6-25-11
On July 20, 2011, the Journal of Internal Medicine e-published ahead of print "Myalgic Encephalomyelitis: International Consensus Criteria."

From "About CFIDS"
By The CFIDS Association of America


Chronic fatigue and immune dysfunction syndrome (CFIDS, also known as chronic fatigue syndrome, CFS, myalgic encephalomyelitis, ME and by many other names) is a complex and debilitating chronic illness that affects the brain and multiple body systems.


Although its name trivializes the illness as little more than mere tiredness, chronic fatigue and immune dysfunction syndrome (CFIDS) brings with it a constellation of debilitating symptoms.

CFIDS is characterized by incapacitating fatigue (experienced as profound exhaustion and extremely poor stamina) and problems with concentration and short-term memory. It is also accompanied by flu-like symptoms such as pain in the joints and muscles, unrefreshing sleep, tender lymph nodes, sore throat and headache. Post-exertional malaise is a hallmark of CFIDS and as the name implies, it is a period of profound fatigue that follows mental or physical activity and requires twenty-four hours (or longer) to recover.

People with CFIDS (PWCs) have symptoms that vary from person to person and fluctuate in severity. Specific symptoms may come and go, complicating treatment and the PWC's ability to cope with the illness. Most symptoms are invisible, which makes it difficult for others to understand the vast array of debilitating symptoms with which PWCs contend.

Additional symptoms are frequently reported by PWC's such as word-finding difficulties, inability to comprehend/retain what is read, inability to calculate numbers and impairment of speech and/or reasoning. PWCs also have visual disturbances (blurring, sensitivity to light, eye pain, need for frequent prescription changes); psychological problems (depression, irritability, anxiety, panic attacks, personality changes, mood swings); chills and night sweats; shortness of breath; dizziness and balance problems; sensitivity to heat and/or cold; alcohol intolerance; irregular heartbeat; irritable bowel (abdominal pain, diarrhea, constipation, intestinal gas); low-grade fever or low body temperature; numbness, tingling and/or burning sensations in the face or extremities; dryness of the mouth and eyes (Sicca aka Sjorgren's syndrome); menstrual problems including PMS and endometriosis; chest pains; rashes; ringing in the ears (tinnitus); allergies and sensitivities to noise/sound, odors, chemicals and medications; weight changes without changes in diet; light-headedness; feeling in a fog; fainting; muscle twitching; and seizures.
[See also CFSupport's MVPS/dysautonomia and orthotatic intolerance list of symptoms.]


Diagnosis of chronic fatigue and immune dysfunction syndrome (CFIDS), also known as chronic fatigue syndrome (CFS), is a time-consuming and difficult process which is generally arrived at by excluding other illnesses with similar symptoms and comparing a patient's symptoms with the 1994 International case definition. As yet, there is no indicator or diagnostic test that can clearly identify the disorder. Overlapping symptoms can occur with several diseases, such as fibromyalgia, Gulf War Illnesses and multiple chemical sensitivities. Many diseases have similar symptoms including lupus, hypothyroidism and Lyme disease and these need to be considered when making a diagnosis.

------------------------------------------------------------------------  End CFIDS Association Excerpt 

Where can I find more description of
Chronic Fatigue Syndrome / Myalgic Encephalomyelopathy (-myelitis)?

About CFIDS - CFIDS Association of America
XMRV News - CFIDS Association of Ameica
MLV News - CFIDS Association of Ameica
About CFS: What is Chronic Fatigue Syndrome? - NIH-Trans Working Group on CFS
About Chronic Fatigue Syndrome - OFFER
An Overview of ME-CFS About ME/CFS
Chronic Fatigue Syndrome - National Women's Health Information Center
Fibromyalgia & Chronic Fatigue Syndrome - Related Syndromes? - Lorden/Carousel Network
An Introduction to Chronic Fatigue Syndrome - Immune Support
ME/CFS - A Basic Overview -
ME/CFS Society Southern Australia 
ME/CFS - An Overview - ME Association
What is ME? ME Research UK
What is ME? ANZMES New Zealand
What is ME/CFS? Network ME
What  is  CFS  -   ME/ CFS ? CFS Information International
What is/Understanding M.E.. and CFS?
The Nightingale Research Foundation, Canada
The Nightingale, M.E. Definition Jan 2007 (PDF) The Nightingale Research Foundation, Canada
CFIDS Fact Sheet 2002 - Mass CFIDS

The Diagnosis of Chronic Fatigue Syndrome:  An Assertive Approach by
Paul R. Cheney, MD, PhD and W. Charles Lapp, MD, FAAP
Help ME - Circle


Official CFS and ME Case Definitions and History

History of CFS/ME Case Definitions - US/International  Mette Marie Andersen, MD, CFS Info
A brief historical account of CFS Case Definitions  Trans-NIH Working Group for CFS
Listing of diagnostic criteria from US and World  Trans-NIH Working Group for CFS

January 2007 Nightingale, M.E. Definition (PDF) The Nightingale Research Foundation, Canada

2005 Myalgic Encephalomyelitis / Chronic Fatigue Syndrome:
A Clinical Case Definition and Guidelines for Medical Practitioners,
An Overview of the Canadian Consensus Document

[was at]

2004 ME/CFS Management Guidelines for General Practitioners (PDF) - Australia

Comparing the Fukuda et al. Criteria and the
Canadian Case Definition for Chronic Fatigue Syndrome (PDF)
  Jason, Journal of CFS

2003 Summary of Canadian Expert Consensus Panel  CFS/ME Clinical Case Definition for CFS/ME (First Clinical Definition) - M.E. Society of America

2003 Carruthers Canadian Myalgic Encephalomyelitis / Chronic Fatigue Syndrome:
Clinical Working Case Definition, Diagnostic and Treatment Protocols
Journal of Chronic Fatigue Syndrome, Vol 11 No 1, Haworth Press

2003 Ambiguities in 1994 Fukuda Case Definition and Recommendations for Resolution

Centers for Disease Control and Prevention: CFS Case Definition (Research)
The Revised Case Definition (abridged version)

1994 Fukuda Research Case Definition (Annals of Internal Medicine)

Myalgic Encephalomyelitis Definitions 1956 - 1994

1957 (Wallis), 1959 (Acheson), 1988 (Ramsay) Research Descriptions of M.E.

CFS Prevalence

Much here is from "About CFIDS"
By The CFIDS Association of America

Summer 2007 cover story of The CFIDS Chronicle:

"Prevalence Figures - How many Americans have CFS? A new study suggests millions. Here is a closer look at the latest numbers and what they could mean."
by K. Kimberly McCleary, CFIDS Association President & CEO

June 2007 - Approximately 4 million in USA!!

Population Health Metrics
"Prevalence of chronic fatigue syndrome in metropolitan, urban, and rural Georgia"
William C Reeves, James F Jones , Elizabeth Maloney, Christine Heim, David C Hoaglin, Roumiana S Boneva, Marjorie Morrissey and Rebecca Devlin

also The CFIDS Association Press Release at


According to the study authors, it is not certain that the prevalence rate found in Georgia can be extrapolated to the entire United States.  But if this rate were to be found to be replicable, the prevalence of adults with CFS in the U.S. would be around 4 million, which is the figure Dr. William Reeves has frequently cited in presentations based on the Georgia study data.  The 7.5 million figure in Peter White’s commentary appears to include all Americans, not Americans between the ages of 18-59, which is the age demographic strictly applicable to the 2.54% prevalence found in Georgia.

For Dr. Jason's comment on problems with this study and prevalance, see

As of late 2006
More than one million Americans have CFS according to studies conducted by researchers at the Centers for Disease Control and Prevention and DePaul University. Approximately 80-90% of patients have not been diagnosed and are not receiving proper medical care for their illness.

As of mid 2006:

A study conducted by researchers at DePaul University estimates CFS at approximately 422 per 100,000 persons in the U.S. [1999] This means as many as 800,000 people nationwide suffer from the illness. 90% of patients have not been diagnosed and are not receiving proper medical care for their illness.

(Jason LA, Richman JA, Rademaker AW, Jordan KM, Plioplys AV, Taylor RR, McCready W, Huang CF, Plioplys S: A Community-Based Study of Chronic Fatigue Syndrome Arch Int Med 1999; 159(18):2129-37.)

CFIDS does not discriminate. 
It strikes people of all age, racial, ethnic, and socioeconomic groups.

Research has shown that CFIDS is about three times as common in women (522/100,000) as men, a rate similar to that of many autoimmune diseases, such as multiple sclerosis and lupus. To put this into perspective, CFIDS is over four times more common than HIV infection in women (125/100,000), and the rate of CFIDS in women is considerably higher than a woman's lifetime risk of getting lung cancer (63/100,000).

From CDC

"More than 1 million Americans suffer from Chronic Fatigue Syndrome (CFS).
Information is available to help identify treatment strategies."

Prevalence and incidence of chronic fatigue syndrome in Wichita, Kansas.
Archives of Internal Medicine 2003;163:1530-1536.

The overall weighted point prevalence of CFS, adjusted for nonresponse, was 235 per 100,000 persons (95% confidence interval, 142-327 per 100,000 persons). The prevalence of CFS was higher among women, 373 per 100,000 persons (95% confidence interval, 210-536 per 100,000 persons), than among men, 83 per 100,000 persons (95% confidence interval, 15-150 per 100,000 persons). Among subjects who were nonfatigued and fatigued for less than 6 months, the 1-year incidence of CFS was 180 per 100,000 persons (95% confidence interval, 0-466 per 100,000 persons).

From a quality paid public awareness ad by the CDC in 2 July 2006 women's magazines,  appearing before the newest research finished its peer review and was published: "More than four million Americans suffer from CFS, and the majority don't know they have it."

What is FMS?

Fibromyalgia syndrome, also called "FMS" or "FM," is a chronic condition of widespread pain, as well as a variety of other symptoms. The name comes from fibro- (fibrous tissues such as tendons and ligaments), -my- (muscle),  -algia (pain) and syndrome for the rest of the symptoms which, for many, also includes fatigue.

The pain of fibromyalgia is often described as diffuse aching or burning, often accompanied by muscle spasm. The pain and the fatigue of fibromyalgia varies from person to person. Fatigue can range from a mild, tired feeling to the exhaustion of a flu-like illness. The pain can vary in degree and migrate, becoming most severe in parts of the body that are used the most (i.e., the neck, shoulders, and feet). In some people, the pain can be intense enough to interfere greatly with work and ordinary, daily tasks, while in others it causes only mild discomfort. 

Symptoms vary from person to person and include 

-stiffness, particularly apparent upon awakening and after prolonged periods of sitting or standing in one position or coinciding with changes in temperature or relative humidity; 
-headaches or facial pain including frequent migraine, tension, vascular headaches, TMJ; 
-sleep disturbances, unrefreshing sleep; 
-digestive disturbances: pain, bloating, constipation, diarrhea, IBS, difficulty swallowing; 
-genito-urinary problems such as increased frequency of urination or increased urgency to urinate, interstitial cystitis (IC), more painful menstrual periods, conditions such as vestibulodynia (vulvar vestibulitis) or vulvodynia, characterized by a painful vulvar region and painful sexual intercourse; 
-numbness or tingling, prickling or burning, particularly, in the hands or feet; 
-skin complaints such as itchy, dry, or blotchy skin, and dryness of the eyes and mouth, a sensation of swelling, particularly in fingers; 
-chest/heart/circulatory/autonomic nervous system imbalance type symptoms such as migrating chest pain, orthostatic intolerance, MVPS/dysautonomia, shallow breathing, unsatisfying breath, dysequilibrium, temperature sensitivity, light-headedness, anxiety and/or depression, balance problems, nausea, visual problems when driving a car, reading a book, or trying to track objects. NMH, POTS, more... see our MVPS/OI page 
-environmental sensitivities including hypersensitivity to light, noise, odors, and weather; 
-cognitive symptoms, nicknamed brain-fog or fibro-fog, including difficulty concentrating, feeling spaced out, short-term memory difficulty, being distracted or overwhelmed easily;
-restless legs, an irresistible urge to move the legs particularly when still too long; 
-exaggerated reactions to a variety of substances including medications, chemicals, food additives, pollutants, etc.

Where can I find more description of Fibromyalgia / Fibromyalgia Syndrome?

About Fibromyalgia  - OFFER
About Fibromyalgia  - National FM & Chronic Pain Association (NFMCPA)
Fibromyalgia & Chronic Fatigue Syndrome - Related Syndromes? - Lorden/Carousel Network
Understanding Fibromyalgia - Immune Support
What is Fibromyalgia? - NIH, NIAMS
What is Fibromyalgia? - Fibromyalgia Coalition International
What is Fibromyalgia Syndrome?  -The FMS Community
What is Fibromyalgia Syndrome? - FM Network
What is Fibromyalgia Syndrome? - National FM Partnership

Official FMS Case Definitions

2010 American College of Rheumatology (ACR) Fibromyalgia Diagnostic Criteria

2005 Fibromyalgia Syndrome
A Clinical Case Definition and Guidelines for Medical Practitioners,
An Overview of the Canadian Consensus Document
[was at]

2003 Fibromyalgia Syndrome
Canadian Clinical Working Case Definition, Diagnostic and Treatment Protocols,
A Consensus Document

The Journal of Musculoskeletal Pain, Volume 11 No 4, Haworth Press

1990 American College of Rheumatology Diagnostic Criteria for the Classification of Fibromyalgia

FM Prevalence

Estimates of the prevalence of arthritis and other rheumatic conditions in the United States: Part II – Source: Arthritis & Rheumatism, Dec 28, 2007
by National Arthritis Data Work Group


Results: We estimated that among US adults:

 711,000 have polymyalgia rheumatica,
 5.0 million have Fibromyalgia,
 4 to 10 million have carpal tunnel syndrome,
 59 million have had low back pain in the past 3 months,
 30.1 million have had neck pain in the past 3 months.

Journal of Clinical Rheumatology. 12(3):124-128, June 2006.

The Incidence of Fibromyalgia and Its Associated Comorbidities: 
A Population-Based Retrospective Cohort Study Based on
International Classification of Diseases, 9th Revision Codes.

"Results: A total of 2595 incident cases of fibromyalgia were identified between 1997 and 2002. Age-adjusted incidence rates were 6.88 cases per 1000 person-years for males and 11.28 cases per 1000 person-years for females. Females were 1.64 times (95% confidence interval = 1.59-1.69) more likely than males to have fibromyalgia. Patients with fibromyalgia were 2.14 to 7.05 times more likely to have one or more of the following comorbid conditions: depression, anxiety, headache, irritable bowel syndrome, chronic fatigue syndrome, systemic lupus erythematosus, and rheumatoid arthritis.

Conclusion: Females are more likely to be diagnosed with fibromyalgia than males, although to a substantially smaller degree than previously reported, and there are strong associations for comorbid conditions that are commonly thought to be associated with fibromyalgia." comments on above study, 07/03/06: 

New Epidemiological Findings Suggest FM Affects 12 Million Americans
First Large Population Analysis Puts Incidence of Fibromyalgia in New Light

The first-ever large population-based analysis of U.S. Fibromyalgia incidence, just released, indicated an occurrence rate of about 4.2 percent.

This is based on a review of claims records for a national health insurance database including a “large, stable” population averaging 62,000 enrollees over the period 1997 through 2002. The new large-population review, conducted by a research team at the University of Utah Department of Family and Environmental Health, identified 2,595 cases of Fibromyalgia in the overall enrollee population.

Their calculations also provide new, more broadly based statistics on:

Fibromyalgia incidence by gender. Females in the database were 1.64 times more likely than the males to have physician-diagnosed Fibromyalgia. That’s a mix of about 62 percent female and 38 percent male; a “substantially” less-marked difference than many small population-based studies had reported.

Strong associations with other, coexisting conditions. Enrollees diagnosed with Fibromyalgia were also significantly more likely than the 59,400-some other health plan enrollees to have one or more of seven coexisting conditions (“comorbidities”). As a group, based on International Classification of Diseases ( ICD-9-CM) diagnostic coding, the Fibromyalgia patients were anywhere from 2.14 times to 7.05 times more likely to have depression, anxiety, headache, irritable bowel syndrome, Chronic Fatigue Syndrome, systemic lupus erythematosus, and rheumatoid arthritis.

From Q&A 8/21/2001 with Roderick S. Hooker, PhD, PA:

"This disorder occurs predominantly in middle-aged women, although the range is reported to be between 8 and 80 years, and both males and females are affected. In industrialized societies FMS affects approximately 2% to 4% of the population.[1,2]"

1) Hooker RS. Treated prevalence of fibromyalgia within an HMO population. Arthritis Rheum. 1987;30:S60.
2) Wolfe F, Ross K, Anderson J, Russell IJ, Hebert L. The prevalence and characteristics of fibromyalgia in the general population. Arthritis Rheum. 1995;38:19-28.


Estimates of the PREVALENCE of Arthritis and Selected Musculoskeletal Disorders in the United States (Wolfe,..., 1998)

"... fibromyalgia is not rare, and it has a potential societal impact in terms of reduced quality of life, decreased functioning in the workplace, and increased utilization of medical services.... 
In summary, available data (Table 9) suggest that the number of persons age 18 and older in the US who have fibromyalgia is approximately 3.7 million. Prevalence is lower in men (0.5%) than in women (3.4). Overall prevalence for adults is approximately 2% and increases with age. The variation in estimates of fibromyalgia prevalence across studies probably reflects the differences in diagnostic or classification criteria ..."


"FMS Monograph"
By The National Fibromyalgia Partnership

Although the exact prevalence of FMS in the general population is difficult to ascertain, up to 10 million Americans have been estimated to have fibromyalgia syndrome,1 and the condition exists around the world. While most prevalent in adult women, fibromyalgia also occurs in children, the elderly, and men.

1. Muhammad Yunus, M.D., "What's New in Fibromyalgia Syndrome? A Review of Abstracts Presented in the 1996 American College of Rheumatology Annual Scientific Meeting: Part 1", The Fibromyalgia Times, Vol. 1, No. 4, Winter 1997, p.4.


Common CFS/FMS Related Acronyms

  • CFIDS - Chronic Fatigue and Immune Dysfunction Syndrome

  • CFS - Chronic Fatigue Syndrome

  • CIND - Chronic Immunological and Neurological Diseases

  • EI - Environmental Illness

  • FM or FMS - Fibromyalgia or Fibromyalgia Syndrome

  • GWI or GWS - Gulf War Illness or Gulf War Syndrome

  • IBD - Inflammatory Bowel Disease

  • IBS - Irritable Bowel Syndrome

  • MCS - Multiple Chemical Sensitivity

  • ME - Myalgic Encephalopathy or Myalgic Encephalomyelitis

  • MPS - Myofascial Pain Syndrome

  • MVPS/D - Mitral Valve Prolapse Syndrome / Dysautonomia

  • NMH - Neurally Mediated Hypotension

  • OI - Orthostatic Intolerance

  • POTS - Postural Orthostatic Tachycardia Syndrome

  • PWC - Person With CFIDS

  • YPWC - Young Person With CFIDS

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Updated March 7, 2013