CFS :: Chronic Fatigue Syndrome
    Symptoms - Diagnostics and Definitions

      The 2003 Canadian ME/CFS Case Definition

The CFS Revised Case Definition from the (abridged version)

In the revised definition, a consensus viewpoint from many of the leading CFS researchers and clinicians (including input from patient group representatives), chronic fatigue syndrome is treated as a subset of chronic fatigue, a broader category defined as unexplained fatigue of greater than or equal to six month's duration. Chronic fatigue in turn, is treated as a subset of prolonged fatigue, which is defined as fatigue lasting one or more months. The expectation is that scientists will devise epidemiologic studies of populations with prolonged fatigue and chronic fatigue, and search within those populations for illness patterns consistent with CFS.


This is the 1994 Definition that was revised?
Fukuda Criteria - Annals Of Internal Medicine:Vol.121; #12 Dec15; 1994 pg 953-959
Full study here

The Chronic Fatigue Syndrome

Major Classification Categories: Chronic Fatigue Syndrome and Idiopathic Chronic Fatigue

Clinically evaluated, unexplained cases of chronic fatigue can be separated into either the chronic fatigue syndrome or idiopathic chronic fatigue on the basis of the following criteria.

A case of the chronic fatigue syndrome is defined by the presence of the following:

1) clinically evaluated, unexplained, persistent or relapsing chronic fatigue that is of new or definite onset (has not been lifelong) is not the result of ongoing exertion; is not substantially alleviatedby rest; and results in substantial reduction in previous levels of occupational, educational, social, or personal activities;


2) the concurrent occurrence of four or more of the following symptoms, all of which must have persisted or recurred during 6 or more consecutive months of illness and must not have predated the fatigue:

  • self-reported impairment in short-term memory or concentration severe enough to cause substantial reduction in previous levels of occupational, educational, social, or personal activities;
  • sore throat;
  • tender cervical or axillary lymph nodes;
  • muscle pain, multi joint pain without joint swelling or redness;
  • headaches of a new type, pattern, or severity; unrefreshing sleep;
  • and post exertional malaise lasting more than 24 hours.

The method used (for example, a predetermined checklist developed by the investigator or spontaneous reporting by the study participant) to establish the presence of these and any other symptoms should be specified.

A case of idiopathic chronic fatigue is defined as clinically evaluated, unexplained chronic fatigue that fails to meet criteria for the chronic fatigue syndrome The reasons for failing to meet the criteria should be specified.

Subgrouping and Stratification of Major Classification Categories

In formal studies, cases of the chronic fatigue syndrome and idiopathic chronic fatigue should be subgrouped before analysis or stratified during analysis by the presence or absence of essential variables, which should be routinely established in all studies. Further subgrouping by optional variables can be done according to specific research interests.

Essential Subgrouping Variables

1. Any clinically important coexisting medical or neuropsychiatric condition that does not explain the chronic fatigue. The presence or absence, classification, and timing of onset of neuropsychiatric conditions should be established using published or freely available instruments, such as the Composite International Diagnostic Instrument (34), the National Institute of Mental Health Diagnostic Interview Schedule (35), and the Structured Clinical Interview for DSM-III(R) (36)

2. Current level of fatigue, including subjective or performance aspects. These levels should be measured using published or widely available instruments. Examples include instruments by Schwartz and colJeagues (37), Piper and colleagues (38), rupp and colleagues (39), Chalder and colleagues (40), and Vercoulen and colleagues (41).

3. Total duration of fatigue.

4. Current level of overall functional performance as measured by published or widely available instruments, such as the Medical Outcomes Study Short Form 36 (42) and the Sickness Impact Profile (43).

Optional Subgrouping Variables

Examples of optional variables include:

1. Epidemiologic or laboratory features of specific interest to researchers. Examples include laboratory documentation or self- reported history of an infectious illness at the onset of fatiguing illness, a history of rapid onset of illness, or the presence or level of a pal1icular immunologic marker.

2. Measurements of physical function quantified by means such as treadmill testing or motion-sensing devices.


from The Revised Case Definition (abridged version)

The Revised Case Definition (abridged version) or
    View Complete Definition


For use in the clinical setting ?

Chronic fatigue syndrome shares symptoms with many other disorders. Fatigue, for instance, is found in hundreds of illnesses, and 10% to 25% of all patients who visit general practitioners complain of prolonged fatigue. The nature of the symptoms, however, can help clinicians differentiate CFS from other illnesses.

Primary Symptoms

As the name chronic fatigue syndrome suggests, this illness is accompanied by fatigue. However, it's not the kind of fatigue patients experience after a particularly busy day or week, after a sleepless night or after a stressful event. It's a severe, incapacitating fatigue that isn't improved by bed rest and that may be exacerbated by physical or mental activity. It's an all-encompassing fatigue that results in a dramatic decline in both activity level and stamina.

People with CFS function at a significantly lower level of activity than they were capable of prior to becoming ill. The illness results in a substantial reduction in occupational, personal, social or educational activities.

A CFS diagnosis should be considered in patients who present with six months or more of unexplained fatigue accompanied by other characteristic symptoms. These symptoms include:

  • cognitive dysfunction, including impaired memory or concentration
  • postexertional malaise lasting more than 24 hours (exhaustion and increased symptoms) following physical or mental exercise
  • unrefreshing sleep
  • joint pain (without redness or swelling)
  • persistent muscle pain
  • headaches of a new type or severity
  • tender cervical or axillary lymph nodes
  • sore throat

Other Common Symptoms

In addition to the eight primary defining symptoms of CFS, a number of other symptoms have been reported by some CFS patients. The frequency of occurrence of these symptoms varies among patients. These symptoms include:

  • irritable bowel, abdominal pain, nausea, diarrhea or bloating
  • chills and night sweats
  • brain fog
  • chest pain
  • shortness of breath
  • chronic cough
  • visual disturbances (blurring, sensitivity to light, eye pain or dry eyes)
  • allergies or sensitivities to foods, alcohol, odors, chemicals, medications or noise
  • difficulty maintaining upright position (orthostatic instability, irregular heartbeat, dizziness, balance problems or fainting)
  • psychological problems (depression, irritability, mood swings, anxiety, panic attacks)
  • jaw pain
  • weight loss or gain

Clinicians will need to consider whether such symptoms relate to a comorbid or an exclusionary condition; they should not be considered as part of CFS other than they can contribute to impaired functioning.

Clinical Course

The severity of CFS varies from patient to patient, with some people able to maintain fairly active lives. By definiton, however, CFS significantly limits work, school and family activities.

While symptoms vary from person to person in number, type and severity, all CFS patients are functionally impaired to some degree. CDC studies show that CFS can be as disabling as multiple sclerosis, lupus, rheumatoid arthritis, heart disease, end-stage renal disease, chronic obstructive pulmonary disease (COPD) and similar chronic conditions.

CFS often follows a cyclical course, alternating between periods of illness and relative well-being. Some patients experience partial or complete remission of symptoms during the course of the illness, but symptoms often reoccur. This pattern of remission and relapse makes CFS especially hard for patients and their health care professionals to manage. Patients who are in remission may be tempted to overdo activities when they're feeling better, which can exacerbate symptoms and fatigue and cause a relapse. In fact, postexertional malaise is a hallmark of the illness.

The percentage of CFS patients who recover is unknown, but there is some evidence to indicate that the sooner symptom management begins, the better the chance of a positive therapeutic outcome. This means early detection and treatment are of utmost importance. CDC research indicates that delays in diagnosis and treatment may complicate and prolong the clinical course of the illness.


Diagnostic Challenges

Diagnosing chronic fatigue syndrome (CFS) can be challenging for health care professionals. A number of factors add to the complexity of making a CFS diagnosis: 1) there's no diagnostic laboratory test or biomarker for CFS, 2) fatigue and other symptoms of CFS are common to many illnesses, 3) CFS is an invisible illness and many patients don't look sick, 4) the illness has a remitting and relapsing course , 5) symptoms vary from person to person infrequency and severity, and 6) no two CFS patients have exactly the same pattern of symptoms.

These factors have contributed to an alarmingly low diagnosis rate. Of the four million Americans who have CFS, less than 20% have been diagnosed.

One has to wonder about the suffering and fate of that other 80%

Overcoming the Challenges

In spite of these challenges, CFS can be diagnosed in a primary care setting. The 1994 International Case Definition for CFS forms the basis of a reliable diagnostic algorithm for CFS, particularly in adults.

While there is evidence that children can get CFS, current research suggests that the illness isn't prevalent in younger children, particularly those under the age of 11. Diagnosing pediatric CFS can be more difficult than adult CFS because children may have difficulty recognizing and verbalizing their symptoms, and because they have a remarkable ability to become accustomed to symptoms and adapt to them. Clinicians assessing adolescents for CFS should exercise judgment based on the course of the illness and the patient's medical history.( long term adult sufferers after time and acceptance of cfs also 'have a remarkable ability to become accustomed to symptoms and adapt to them'

How Physicians Diagnose CFS

If a patient has had 6 or more consecutive months of severe fatigue that is reported to be unrelieved by sufficient bed rest and that is accompanied by nonspecific symptoms, including flu-like symptoms, generalized pain, and memory problems, the physician should further investigate the possibility that the patient may have CFS. The first step in this investigation is obtaining a detailed medical history and performing a complete physical examination of the patient. Initial testing should include a mental status examination, which ordinarily will involve a short discussion in the office or a brief oral test. A standard series of laboratory tests of the patient's blood and urine should be performed to help the physician identify other possible causes of illness. If test results suggest an alternative explanation for the patient's symptoms, additional tests may be ( should be, have to be )performed to confirm that possibility. If no cause for the symptoms is identified, the physician may render a diagnosis of CFS if the other conditions of the case definition are met. A diagnosis of insufficient fatigue (ISF) could be made if a patient has been fatigued for 6 months or more, but does not meet the symptom criteria for CFS.

An Empirical Definition

Recently the definitional criteria have reached using information derived from 3 questionnaires: MOS SF-36, Multidimensional Fatigue Inventory, and the CDC Symptom Inventory (Reeves et al, 2005). This approach can be useful in identifying patient and in monitoring their illness course or response to treatment.

Appropriate Tests for Routine Diagnosis of CFS

While the number and type of tests performed may vary from physician to physician, the following tests constitute a typical standard battery to exclude other causes of fatiguing illness: alanine aminotransferase (ALT), albumin, alkaline phosphatase (ALP), blood urea nitrogen (BUN), calcium, complete blood count, creatinine, electrolytes, erythrocyte sedimentation rate (ESR), globulin, glucose, phosphorus, thyroid stimulating hormone (TSH), total protein, transferrin saturation, and urinalysis. Further testing may be required to confirm a diagnosis for illness other than CFS. For example, if a patient has low levels of serum albumin together with an above-normal result for the blood urea nitrogen test, kidney disease would be suspected. The physician may choose to repeat the relevant tests and possibly add new ones aimed specifically at diagnosing kidney disease. If autoimmune disease is suspected on the basis of initial testing and physical examination, the physician may request additional tests, such as for antinuclear antibodies.


The name "chronic fatigue syndrome" is the final issue that we wish to address. We sympathize with those who are concerned that this name may trivialize this illness. The impairments associated with chronic fatigue syndrome are not trivial. However, we believe that changing the name without adequate scientific justification will lead to confusion and will substantially undermine the progress that has been made in focusing public, clinical, and research attention on this illness. We support changing the name when more is known about the underlying pathophysiologic process or processes associated with the chronic fatigue syndrome and chronic fatigue.

Note: This could occur when sub-types start to be finally identified and defined


When people with CFS develop significant new symptoms, or experience a marked change in symptoms, they should be carefully reassessed by a health professional.
New symptoms should not automatically be assumed to be part of the CFS symptom complex.

There has been a lack of consistency in CFS laboratory findings, which may be a function of combining distinctive groups of patients into a large heterogeneous group rather than analyzing them within subtypes. In reality, there rarely is a perfect biological test for an illness, but with CFS there does appear to be mounting evidence of brain and immune system abnormalities
(Komaroff, 2000).

MAY 12   2009

Awareness Day

In summary, CFS and depression are two distinct disorders, although they share a number of common symptoms. Most importantly, the erroneous inclusion of people with primary psychiatric conditions in CFS samples will have detrimental consequences for the interpretation of both epidemiologic and treatment efficacy findings. (Jason et al 2005)


ME/CFS International Awareness Day

Return to Home page  | Contacts | Newsletters |
Email  |  |