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Fukuda Criteria - Annals Of Internal Medicine:Vol.121; #12 Dec15; 1994 pg 953-959

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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.


Several general points must be appreciated if these guidelines are to be used as intended. First, the overall purpose of the proposed conceptual framework and guidelines is to foster a more systematic and comprehensive approach toward the collection of data about the chronic fatigue syndrome and similar illnesses. As such, these tools are intended for use as standard references. However, none of the components, including the revised case definition of the chronic fatigue syndrome, can be considered definitive. These research tools will evolve as new knowledge is gained. Second, none of the provisions in these guidelines, especially the definition of idiopathic chronic fatigue and subgroups of the chronic fatigue syndrome, establish new clinical entities. Rather, these definitions were designed to facilitate comparative studies. Finally, general reference to these guidelines should not be substituted for clear and detailed methodologic descriptions when reporting studies. The lack of detailed information about the sources, selection, and evaluation of study participants (including controls), case definitions, and measurement techniques in reports of chronic fatigue syndrome research has contributed substantially to our current difficulties in interpreting research findings.

Several specific points about the clinical evaluation are worth emphasizing. The primary purpose of clinically evaluating a person with unexplained fatigue is to identify and treat any underlying and contributing factors. Such an evaluation should begin, whenever possible, before 6 months have elapsed. Because the particulars of any clinical evaluation will vary from patient to patient our recommendations have been limited to those aspects of clinical evaluation that can be universally applied to all patients With regard to the clinical psychiatric evaluation of fatigued persons, we consider a mental status examination to be the minimal acceptable level of assessment. Although a structured psychiatric evaluation of all patients with fatigue is highly desirable, we recognize the practical difficulties of implementing such a recommendation. Diagnosis of the chronic fatigue syndrome should not impede the treatment of coexisting disorders, notably depression.

Many conditions that are primary causes of chronic fatigue preclude the diagnosis of the chronic fatigue syndrome or idiopathic chronic fatigue. We presented principles for identifying such exclusionary conditions rather than listing them because of the range and complexity of human illnesses In some instances, however, we identified specific exclusionary conditions The presence of severe obesity makes the diagnosis of unexplained symptoms, such as fatigue or joint pains, extremely difficult. We distinguished between psychiatric conditions for pragmatic reasons. It is difficult to interpret symptoms typical of the chronic fatigue syndrome in the setting of illnesses such as major psychotic depression or schizophrenia. More importantly, care of these persons should focus on their chronic psychiatric disorder.

On the other hand, we did not use other psychiatric disorders, such as anxiety disorders and less severe forms of depression, as a basis for exclusion. Such psychiatric conditions are highly prevalent in persons with chronic fatigue and the chronic fatigue syndrome, and the exclusion of persons with these conditions would substantially hinder efforts to clarify the role that psychiatric disorders have in fatiguing illnesses. This is a particularly important issue to resolve. These parts of the guidelines concur with the recommendation by a 1991 National Institutes of Health workshop (24) that chronic fatigue cases preceded by some, but not all, psychiatric syndromes can be classified as the chronic fatigue syndrome.

The revised case definition for the chronic fatigue syndrome is modeled on the 1988 chronic fatigue syndrome working case definition (l). The purpose of our revisions was to address some of the criticisms (25) of that case definition and to facilitate a more systematic collection of data internationally. We dropped a1l physical signs from our inclusion criteria because we agreed that their presence had been unreliably documented in past studies. The required number of symptoms was decreased from 8 to 4 and the list of symptoms was decreased from 11 to 8 because we agreed that multiple symptom criteria had increased the restrictiveness of the 1988 chronic fatigue syndrome working case definition without increasing the homogeneity of cases (Reyes M, et aI. Unpublished data). Whether to retain any symptom criteria other than chronic fatigue generated the most disagreement among the authors.

Disagreement occurred between those who favored a more restrictive approach (using several symptom criteria), as was done in the 1988 chronic fatigue syndrome working case definition, and those who favored a broader definition of chronic fatigue syndrome (using fewer symptom criteria) as was done in the Australian (3) and British (4) chronic fatigue syndrome case definitions. Those favoring multiple symptoms argued that use of multiple symptoms best reflected the empiric clinical sense of the chronic fatigue syndrome as a distinct entity. Others argued that no symptoms have been shown to be specific for the chronic fatigue syndrome (28) and that some studies suggest that a requirement for multiple symptoms biases the selection of cases toward those with psychiatric disorders (28, 44) Disagreement over this particular issue underscores the need to establish specific features of the chronic fatigue syndrome and the validity of any chronic fatigue syndrome case definition.

Developing an operational definition of fatigue was a problem because the concept of fatigue itself is unclear (45, 46). In our conception of the chronic fatigue syndrome, the symptom of fatigue' refers to severe mental and physical exhaustion, which differs from somnolence or lack of motivation and which is not attributable to exertion or diagnosable disease. We retained the requirement of 6 months' duration of fatigue to facilitate comparison with earlier cases of the chronic fatigue syndrome The requirement for an "average daily activity below 50%" was eliminated because this level of impairment is difficult to verify

We defined the condition of "idiopathic chronic fatigue"_ to focus attention on the need to clarify how other forms of unexplained chronic fatigue are related to the chronic fatigue syndrome

Our strategy for subgrouping major classification categories depends on the data made available 6'om standardized evaluations of patients with chronic fatigue. Subgrouping by essential variables wiIl encourage the collection of a body of core data. Additional subgrouping by optional variables will allow researchers considerable flexibility in defining specific subgroups to answer specific research questions.

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 wiIl 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.

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