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Source: Journal of Clinical Psychology in Medical Settings Vol. 8, No. 4, pp 337-343 Date: December 2001

Leonard A. Jason,(1,2) Susan R. Torres-Harding,(1) Renee R. Taylor,(1) and Adam W. Carrico(1)

Chronic Fatigue Syndrome (CFS) is an illness that involves severe, prolonged fatigue as well as neurological, immunological, and endocrinological system pathology (Friedberg & Jason, 1998). Despite years of research, CFS remains a poorly understood and controversial disease (Jason, et al., 1995). CFS has been difficult to define because the exact causal agents are unknown, physical signs and symptoms are variant, and diagnostic laboratory tests have poor sensitivity and specificity (Bates et al., 1992; Holmes, 1991).

In 1988, Holmes, Kaplan, Gantz, et al. (1988) constructed the first U.S. working case definition of CFS. However, as the 1988 criteria were utilized in research and practice, it became evident that there were numerous inconsistencies in interpretation and classification (Holmes, Kaplan, Gantz, et al., 1988; Matthews, Lane, & Manu, 1988; Schluederberg, et al., 1992; Straus, 1992). Katon, Buchwald, Simon, Russo, and Mease (1991) found that patients with CFS were indistinguishable from those with symptoms of chronic fatigue not meeting the 1988 CDC criteria. A major area of concern with the original CFS criteria was that the requirement of eight or more minor symptoms could inadvertently select for individuals with psychiatric problems (Straus, 1992). Katon and Russo (1992) noted that chronic fatigue patients with the highest number of unexplained physical symptoms had very high rates of psychiatric disorders whereas patients with the lowest number of unexplained symptoms displayed rates of psychiatric disorders that were similar to other clinic populations with chronic medical illness.

These difficulties were influential in the development of a revised U.S. case definition for CFS by Fukuda et al. (1994). In this revised 1994 definition, a patient is required to experience chronic fatigue of a new or definite onset (for 6 or more months), that is not substantially alleviated by rest, not the result of ongoing exertion, and produces significant reductions in occupational, social, or personal activities. The 1994 criteria also require the concurrent occurrence of at least four of eight minor symptoms.

Several investigations have contrasted the two U.S. case definitions of CFS.  In a study of 2,376 primary care patients, 1.2% of the sample were diagnosed with CFS by using the 1988 case definition, compared to 2.6% using the 1994 case definition (Wessely, Chalder, Hirsch, Wallace, & Wright, 1997). Tiersky et al. (2000) investigated the differences between the 1988 and 1994 case definition criteria in a study of 71 primary care patients with CFS.  Participants meeting only the 1994 definition experienced a greater duration of illness than those meeting the 1988 definition. In contrast, those in the 1988 group reported greater frequency of sore throats, joint pain, tender lymph nodes, headaches, and fever. Finally, the 1988 group was more likely to report a sudden illness onset and a greater reduction in premorbid activity levels than the 1994 group.

In the present study, patients diagnosed with CFS according to the more stringent 1988 criteria were compared to those who met only the 1994 criteria and to those with fatigue due to psychiatric causes on measures of psychiatric comorbidity, symptom frequency, and functional impairment. It was hypothesized that the 1988 criteria, in comparison to the 1994 criteria, would identify a patient group with more psychiatric comorbidity, symptoms, and functional impairment.


METHOD

Procedure

The data was derived from a larger community-based study of CFS carried out in three stages (Jason, Richman, et al., 1999). Stage 1 entailed a cross-sectional screening telephone survey of a random sample of 28,673 households, with 18,675 adults completing the screening interview (65.1% completion rate). Stage 2 involved a structured psychiatric interview for those respondents from Stage 1 who screened positive for CFS (i. e., 6 or more months of fatigue, and at least four minor symptoms based on the Fukuda et al., 1994, CFS criteria). In Stage 3, a physician conducted a detailed medical examination to rule out exclusionary medical conditions. A team of four physicians and a psychiatrist were responsible for making a final diagnosis, with two physicians independently rating each file, using the current U. S. case definition of CFS. Where physicians disagreed, a third physician rater was used (see Jason, Richman et al., 1999).  For the purpose of the present study, we focus on those 32 individuals who were diagnosed with CFS by using the 1994 Fukuda case definition, and 33 with chronic fatigue explained by psychiatric reasons (CF-Psychiatric). (3)


Definitions

1988 Criteria

To be classified with fatigue according to the 1988 criteria (Holmes, Kaplan, Gantz, et al., 1988), participants needed to report 6 or more months of persistent or relapsing, debilitating fatigue that does not resolve with bed rest. Also, participants were required to report at least 8 of 11 minor symptoms (fever or chills, sore throat, lymph node pain, muscle weakness, muscle pain, postexertional malaise, headaches of a new or different type, migratory arthralgias, neuropsychiatric complaints, sleep disturbance, and a sudden onset of symptoms).  Participants were also required to report at least a 50% impairment of daily functioning, as compared to premorbid levels.  Exclusionary criteria, as defined by Holmes, Kaplan, Gantz, et al. (1988) and Holmes, Kaplan, Schonberger, et al. (1988), were used. Fourteen of the 32 individuals diagnosed with CFS by using the Fukuda's 1994 criteria, also met the more stringent 1988 criteria.


1994 Criteria

Physicians utilized the current U. S. case definition in their diagnoses of CFS after a thorough medical examination (Fukuda et al., 1994). To be diagnosed with CFS, participants were required to experience persistent or relapsing fatigue for a period of 6 or more months as well as the concurrent occurrence of four or more minor symptoms that did not predate the illness and persisted for 6 or more months since onset.  Minor symptoms of the current U.S. case definition of CFS included sore throat, lymph node pain, muscle pain, joint pain, postexertional malaise, headaches of a new or different type, memory and concentration difficulties, and unrefreshing sleep.  Furthermore, the participant had to experience substantial reductions in occupational, educational, social, or personal activities as a result of their illness. Exclusionary illnesses as defined by Fukuda et al. (1994) were used.  As mentioned earlier, 32 individuals were diagnosed with these criteria.


A Comparison of Diagnostic Criteria

Measures

Symptom Occurrence

Participants were also asked to complete the CFS Symptom Rating Form. Using this form, participants indicated whether the eight CFS definitional symptoms (Fukuda et al., 1994) occurred over the last 6 months constantly or repeating regularly. Jason, Ropacki, et al. (1997) used a modified version of this form, which was demonstrated to have high test-retest reliability over a 2-week period (test-retest agreement: 76-92%).


Medical Outcomes Study

Participants completed the Medical Outcomes Study 36-item Short-Form Survey (MOS) (Ware & Sherbourne, 1992; Ware, Snow, Kosinski, & Gandek, 2000), a reliable and valid measure that discriminates between gradations of disability. This instrument encompasses multi-item scales that assess physical functioning, role limitations, social functioning, bodily pain, general mental health, vitality, and general health perceptions. Higher scores indicated better health, lower disability, or less impact of health on functioning. Reliability and validity studies for the 36-item version of the MOS have shown adequate internal consistency, discriminant validity among subscales, and substantial differences between patient and non-patient populations in the pattern of scores (McHorney, Ware, Lu, & Sherbourne, 1994; McHorney, Ware, & Raczek, 1993; McHorney, Ware, Rogers, Razek, &Lu, 1992). The MOS Physical Composite Score (PCS) and Mental Composite Score (MCS) were also utilized in the present investigation as combined measures of the eight MOS subscales to rate overall impairment of functioning (Ware, Kosinski, & Keller, 1994).  These PCS and MCS have appropriate validity and reliability as well as greater sensitivity and specificity in discriminating the gradations of health status among groups (Brazier et al., 1992).


Degree of Impairment

Participants were asked to rate the degree to which their fatigue has impaired their functioning in daily activities on a 100-point scale, with 0= no difficulties and 100= total and complete disability.

Psychiatric Diagnoses

The Structured Clinical Interview for the DSM-IV (SCID) (Spitzer, Williams, Gibbon, & First, 1995) was administered to provide current and lifetime psychiatric diagnoses as defined on Axis I of the Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV) (American Psychiatric Association, 1994). The SCID is a valid and reliable measure semi-structured interview that approximates a psychiatric interview (Rubinson & Asnis, 1989).  Trained advanced clinical psychology graduate students with master's degrees administered the SCID. The SCID provides for specification of current and past psychiatric disorders. Using this specification of current and past disorders, two indices were developed to indicate if a person met criteria for at least one current psychiatric disorder, and if a participant met criteria for at least one lifetime (i. e., past or current) psychiatric disorder.


RESULTS

Thirty-two participants were diagnosed with CFS, using Fukuda et al.  (1994) case definition; 14 also met the more stringent 1988 criteria (Holmes, Kaplan, Gantz, et al., 1988). Comparisons were made between the 14 participants who met the 1988 criteria (1988 group), the 18 participants who met only the 1994 criteria (1994 only group), and the 33 participants whose fatigue was explained by a psychiatric illness (CF psychiatric group).

Using chi-square analyses, participants in the 1988, 1994, and CF Psychiatric groups did not significantly differ on socio-demographic variables or the sudden onset of symptoms (See Table I). However, the 1988, 1994, and CF Psychiatric groups differed significantly in rates of current, chi^2(1,64)=8.64, p<.05, and lifetime chi^2(1,64)=7.41, p<.05, psychiatric diagnoses.  The 1988 and 1994 groups only had significantly fewer current and lifetime psychiatric diagnoses than the CF Psychiatric group.

Chi-square analyses were performed to examine the overall differences among the 1988, 1994, and CF Psychiatric groups for the occurrence of the eight minor symptoms in the current U. S. case definition of CFS (see Table II).  Results indicated that the groups differed significantly overall in the frequency of sore throat pain, chi^2(2, 65)=6.27, p<.05, and lymph node pain chi^2(2, 65)=15.54, p<.01. The 1988 group reported significantly higher rates of sore throat pain and lymph node pain than the 1994 group.  Furthermore, those participants meeting the 1988 criteria had significantly higher rates of sore throat pain and lymph node pain than the CF Psychiatric group.

One-way ANOVAs were conducted examining MOS scores and participant ratings of impairment of functioning in daily activities.  These analyses were significant overall for the general health subscale of the MOS, F(2,57)=3.18, p<.05; the bodily pain subscale of the MOS, F(2,60)=3.16, p=.05; the PCS, F(2,50)=3.81, p<.05; and participant self ratings of impairment of functioning in daily activities, F(2,59)=4.82, p<.05. Bonferroni post hoc analyses indicated that participants in the 1988 group had poorer general health functioning than those in the 1994 group only. The 1988 group also had significantly more bodily pain and lower PCS scores than the CF Psychiatric group. Finally, in the self-reports of the degree of impairment of functioning in daily activities, the 1994 group only reported significantly less impairment than the CF Psychiatric group.


DISCUSSION

This study examined differences in socio-demographic characteristics, symptom frequency, and functional impairment with individuals meeting different diagnostic criteria sets for CFS. When samples of individuals meeting each of the two U. S. definitional criteria for CFS were compared (1988 vs. 1994), findings revealed no socio-demographic or psychiatric differences between the two samples.   However, important differences did emerge between the two CFS diagnostic groups with respect to symptom frequency and functional impairment.  Our findings indicate that the 1988 group is more impaired in measures of symptom frequency as well as functional impairment. This suggests that the 1988 criteria appears to select a more symptomatic and impaired group of individuals than the 1994 and psychiatrically fatigued groups.

Results are consistent with Tiersky et al. (2000), who also found increased occurrence of sore throat pain and lymph node pain in the 1988 group when compared to the 1994 group. However, Tiersky et al. (2000) also reported that the 1988 group was more significantly likely to experience joint paint and headaches when compared to the 1994 group only. Upon closer examination, the frequency of the 1994 definitional symptoms reported in the Tiersky study is generally higher in the 1988 group than the reported occurrence of these symptoms in the present investigation's 1988 group. Additional findings reported by Tiersky et al. (2000) may be due to their clinic-based sample such that participants could have experienced a more severe illness with a greater number of symptoms.

In relation to the two U.S. CFS criteria groups, the CF-explained psychiatric group evidenced less symptom frequency, and less functional impairment than the 1988 group, but perceived themselves more functionally impaired than the 1994 group. Predictably, the CF-explained psychiatric group also evidenced the highest frequency of current and lifetime psychiatric disorders.

A central strength of this study is that it is the first of its kind to use random epidemiological methods to empirically compare the 1988 and the 1994 diagnostic criteria for CFS. It also re-examines the role of psychiatric disorders in relation to different diagnostic criteria sets.  Findings should be interpreted within the context of limitations on statistical power imposed by a small sample size. Because some differences between groups may have not been detected, more research with larger samples is necessary to replicate these results.

Studies examining sources of diagnostic unreliability have shown that subject, occasion, and information variance account for only a small portion of diagnostic reliability (Spitzer, Endicott, & Robins, 1975).  However, criterion variance, differences in the formal inclusion and exclusion criteria used by clinicians to classify patients' data into diagnostic categories, accounts for the largest source of diagnostic unreliability.  The two U.S. definitions of CFS would be improved if more attention was devoted to developing operationally explicit, objective criteria and standardized interviews (Jason, King, et al., 1999).

In summary, participants meeting the 1988 criteria appear to be a more symptomatic and functionally impaired group than those meeting the 1994 criteria only. Furthermore, these differences do not appear to be influenced by psychiatric variables, as they occurred in the absence of differences in rates of psychiatric comorbidity between the two groups. Taken together, these findings indicate that the 1988 criteria may identify a distinct group of individuals who not only have a higher frequency of CFS symptoms, but also experience greater functional disability. Possibly because of the lesser degree of specificity in criteria, individuals in the 1994 group may comprise more heterogeneous patient groups experiencing more variability and wider ranges of illness severity and functional disability.


ACKNOWLEDGMENT

Financial support for this study was provided by NIAID Grant No. AI36295.

TABLES

FOOTNOTES

REFERENCES

(c) 2001 Kluwer

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