Chronic fatigue syndrome: symptom subtypes in a community based sample

Epstein-Barr Virus Induced Gene-2 Upregulation Identifies a Particular Subtype of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) is a chronic multisystem disease characterized by a variety of symptoms, and exhibits various features of an autoimmune-like disease. Subtypes are well recognized but to date are difficult to identify objectively. The disease may be triggered by infection with a variety of micro-organisms, including Epstein-Barr virus (EBV). A subset of CFS/ME patients exhibit up regulation of EBV virus induced gene 2 (EBI2) mRNA in peripheral blood mononuclear cells (PBMC), and these patients appear to have a more severe disease phenotype and lower levels of EBNA1 IgG. EBI2 is induced by EBV infection and has been found to be upregulated in a variety of autoimmune diseases. EBI2 is a critical gene in immunity and central nervous system function; it is a negative regulator of the innate immune response in monocytes. Its heterogeneous expression in CFS/ME could explain the variable occurrence of a variety of immune and neurological abnormalities which are encountered in patients with CFS/ME. The EBI2 subtype occurred in 38-55% CFS/ME patients in our studies. Further work is required to confirm the role of EBV and of EBI2 and its oxysterol ligands in CFS/ME, and to identify the most practical means to identify patients of the EBI subtype. There are two EBI2 antagonists currently in development, and these may hold promise in the treatment of CFS/ME patients of the EBI subtype.

The aetiopathogenesis of fatigue: unpredictable, complex and persistent

BACKGROUND

Chronic fatigue syndrome is a common condition characterized by severe fatigue with post-exertional malaise, impaired cognitive ability, poor sleep quality, muscle pain, multi-joint pain, tender lymph nodes, sore throat or headache. Its defining symptom, fatigue is common to several diseases.

AREAS OF AGREEMENT

Research has established a broad picture of impairment across autonomic, endocrine and inflammatory systems though progress seems to have reached an impasse.

AREAS OF CONTROVERSY

The absence of a clear consensus view of the pathophysiology of fatigue suggests the need to switch from a focus on abnormalities in one system to an experimental and clinical approach which integrates findings across multiple systems and their constituent parts and to consider multiple environmental factors.

GROWING POINTS

We discuss this with reference to three key factors, non-determinism, non-reductionism and self-organization and suggest that an approach based on these principles may afford a coherent explanatory framework for much of the observed phenomena in fatigue and offers promising avenues for future research.

AREAS TIMELY FOR DEVELOPING RESEARCH

By adopting this approach, the field can examine issues regarding aetiopathogenesis and treatment, with relevance for future research and clinical practice.

Severity Scales for Use in Primary Health Care to Assess Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is a physical and cognitive disabling illness, characterized by severe fatigue and a range of physiological symptoms, that primarily affects women. The immense variation in clinical presentation suggests differences in severity based on symptomology and physical and cognitive functional capacities. In this article, we examine a number of severity scales used in assessing severity of patients with CFS/ME and the clinical aspects of CFS/ME severity subgroups. The use of severity scales may be important in CFS/ME because it permits the establishment of subgroups that may improve accuracy in both clinical and research settings.

Cumulative fatigue symptoms among caregivers in Japan

OBJECTIVE

To investigate the relationship of cumulative fatigue symptoms among caregivers in Japan with work environment issues and lifestyle behaviors.

METHODS

The subjects were 376 women (mean age, 54 years) attending professional seminars for caregivers held between 1999 and 2002. After obtaining informed consent, a survey was conducted to ascertain work environment issues, lifestyle behaviors and fatigue levels. Fatigue was quantitatively assessed using the Cumulative Fatigue Symptoms Index (CFSI) developed by Kosugoh et al. Factors related to caregiver fatigue were identified using Pearson's correlation coefficient, the Mann-Whitney U-test and multiple regression analysis.

RESULTS

Caregivers who felt an xiety or concern regarding care techniques, care content, personal relationships, work conditions, and physical fitness showed higher CFSI scores, while caregivers who exercised regularly and had proper eating behavior displayed lower CFSI scores. Anxiety/concern regarding physical fitness and proper eating behaviors were identified as significant predictors for all CFSI category scores (P<0.001). Regular exercise behavior (P<0.001), age (P<0.001), and years of work experience (P<0.001) also represented significant independent variables for some CFSI categories.

CONCLUSION

Our results suggest that upgrading the knowledge and skills of care and nursing and modifying lifestyle behaviors could reduce the level of fatigue experienced by caregivers.

Psycho-physiological impact on women with chronic fatigue syndrome in the context of their couple relationship

The quality of dyadic adjustment is likely to play an important role in patients' relational problems and may also be associated with the clinical presentation of chronic fatigue syndrome (CFS) symptoms. The objective of this study was (1) to determine whether CFS patients and their partners have similar perceptions of their dyadic adjustment and (2) to evaluate whether the influence of dyadic satisfaction in women with CFS, as well as common psychological parameters such as anxiety, may correlate with physiological responses at rest and/or when performing very low intensity exercise. Forty females with CFS and their partners completed the Dyadic Adjustment Scale, the State-Trait Anxiety Inventory, and the Hospital Anxiety and Depression scale. The cardiovascular adaptation of patients was evaluated during resting conditions and on a precalibrated cycle ergometer while performing very low intensity exercise. Patients and partners had similar perceptions of their marital relationship. Both at rest and during very low workload, various physiological parameters in the patient group showed statistical correlations with certain psychological parameters. Several psychological variables, such as anxiety and dyadic adjustment, were associated with the cardioventilatory response monitored at rest and during very low intensity exercise. Further studies are needed to determine the nature of this association.

Chronic fatigue syndrome: illness severity, sedentary lifestyle, blood volume and evidence of diminished cardiac function

The study examined whether deficits in cardiac output and blood volume in a CFS (chronic fatigue syndrome) cohort were present and linked to illness severity and sedentary lifestyle. Follow-up analyses assessed whether differences in cardiac output levels between CFS and control groups were corrected by controlling for cardiac contractility and TBV (total blood volume). The 146 participants were subdivided into two CFS groups based on symptom severity data, severe (n=30) and non-severe (n=26), and two healthy non-CFS control groups based on physical activity, sedentary (n=58) and non-sedentary (n=32). Controls were matched to CFS participants using age, gender, ethnicity and body mass. Echocardiographic measures indicated that the severe CFS participants had 10.2% lower cardiac volume (i.e. stroke index and end-diastolic volume) and 25.1% lower contractility (velocity of circumferential shortening corrected by heart rate) than the control groups. Dual tag blood volume assessments indicated that the CFS groups had lower TBV, PV (plasma volume) and RBCV (red blood cell volume) than control groups. Of the CFS subjects with a TBV deficit (i.e. > or = 8% below ideal levels), the mean+/-S.D. percentage deficit in TBV, PV and RBCV were -15.4+/-4.0, -13.2+/-5.0 and -19.1+/-6.3% respectively. Lower cardiac volume levels in CFS were substantially corrected by controlling for prevailing TBV deficits, but were not affected by controlling for cardiac contractility levels. Analyses indicated that the TBV deficit explained 91-94% of the group differences in cardiac volume indices. Group differences in cardiac structure were offsetting and, hence, no differences emerged for left ventricular mass index. Therefore the findings indicate that lower cardiac volume levels, displayed primarily by subjects with severe CFS, were not linked to diminished cardiac contractility levels, but were probably a consequence of a co-morbid hypovolaemic condition. Further study is needed to address the extent to which the cardiac and blood volume alterations in CFS have physiological and clinical significance.

Replication of an empirical approach to delineate the heterogeneity of chronic unexplained fatigue

BACKGROUND

Chronic fatigue syndrome (CFS) is defined by self-reported symptoms. There are no diagnostic signs or laboratory markers, and the pathophysiology remains inchoate. In part, difficulties identifying and replicating biomarkers and elucidating the pathophysiology reflect the heterogeneous nature of the syndromic illness CFS. We conducted this analysis of people from defined metropolitan, urban, and rural populations to replicate our earlier empirical delineation of medically unexplained chronic fatigue and CFS into discrete endophenotypes. Both the earlier and current analyses utilized quantitative measures of functional impairment and symptoms as well as laboratory data. This study and the earlier one enrolled participants from defined populations and measured the internal milieu, which differentiates them from studies of clinic referrals that examine only clinical phenotypes.

METHODS

This analysis evaluated 386 women identified in a population-based survey of chronic fatigue and unwellness in metropolitan, urban, and rural populations of the state of Georgia, USA. We used variables previously demonstrated to effectively delineate endophenotypes in an attempt to replicate identification of these endophenotypes. Latent class analyses were used to derive the classes, and these were compared and contrasted to those described in the previous study based in Wichita, Kansas.

RESULTS

We identified five classes in the best fit analysis. Participants in Class 1 (25%) were polysymptomatic, with sleep problems and depressed mood. Class 2 (24%) was also polysymptomatic, with insomnia and depression, but participants were also obese with associated metabolic strain. Class 3 (20%) had more selective symptoms but was equally obese with metabolic strain. Class 4 (20%) and Class 5 (11%) consisted of nonfatigued, less symptomatic individuals, Class 4 being older and Class 5 younger. The classes were generally validated by independent variables. People with CFS fell equally into Classes 1 and 2. Similarities to the Wichita findings included the same four main defining variables of obesity, sleep problems, depression, and the multiplicity of symptoms. Four out of five classes were similar across both studies.

CONCLUSION

These data support the hypothesis that chronic medically unexplained fatigue is heterogeneous and can be delineated into discrete endophenotypes that can be replicated. The data do not support the current perception that CFS represents a unique homogeneous disease and suggests broader criteria may be more explanatory. This replication suggests that delineation of endophenotypes of CFS and associated ill health may be necessary in order to better understand etiology and provide more patient-focused treatments.

The relationship between fatigue and cardiac functioning

BACKGROUND

Although characteristics such as heart rate (HR) and blood pressure (BP) are commonly reported in studies of the relationship between fatigue and cardiac functioning, few reports examine how cardiac function parameters such as cardiac output (CO) and stroke volume (SV) relate to fatigue. This study examined the relationship between self-reported fatigue and hemodynamic functioning at rest and in response to a public speaking stressor in healthy individuals.

METHODS

A total of 142 individuals participated in this study. Subjects were placed in low-, moderate-, or high-fatigue groups based on their Profile of Moods State fatigue scale. Heart rate, SV, and CO were determined using impedance cardiography at rest and during a speaking stressor. Stroke volume and CO values were converted to stroke index (SI) and cardiac index (CI) by adjusting for body surface area. Data were analyzed with hierarchical regression analysis and a 3 (group) x 3 (stress period) mixed model analysis of variance.

RESULTS

At rest, fatigue was not associated with BP or HR but was significantly associated with decreased CI (P < .001; 95% confidence interval, -0.046 to -0.014) and stroke index (SI) (P = .002; 95% confidence interval -0.664 to -0.151), even after controlling for demographic variables and depressive symptoms. Heart rate and BP increased, as expected, from baseline to preparation to speaking stressor (F (1,124) = 118.6 and F (1,122) = 46.450, respectively) (P < .001 for both). More interestingly, there were effects on SI and CI of fatigue (P<.03 for both) and stress (P<.03 for both); high-fatigue individuals had lower SI and CI levels than moderate- and low-fatigue individuals both at rest and in response to the stressor.

CONCLUSION

This study demonstrates that fatigue complaints may have hemodynamic correlates even in ostensibly healthy individuals.

The validity of an empirical delineation of heterogeneity in chronic unexplained fatigue

OBJECTIVES

To validate a latent class structure derived empirically from a clinical data set obtained from persons with chronic medically unexplained fatigue.

METHODS

The strategies utilized in this validation study included: recalculating latent class analysis (LCA) results varying random seeds and the number of initial random starting sets; recalculating LCA results by substituting alternate variables to demonstrate a robust solution; determining the statistical significance of between-class differences on disability, fatigue and demographic measures omitted from the data set used for LCA; cross-classifying class membership using established Centers for Disease Control and Prevention (CDC) research criteria for chronic fatigue syndrome (CFS) to compare the relative proportions of subjects designated CFS, chronic fatigue (not CFS) or healthy controls captured by the latent classes.

RESULTS

Recalculation of results and substitution of variables for low-loading variables demonstrated a robust LCA result. Highly significant between-class differences were confirmed between Class 2 (well) and those interpreted as ill/fatigued. Analysis of between-class differences for the fatigue groups revealed significant differences for all disability and fatigue variables, but with equivalent levels of reported activity and reduction in motivation. Cross-classification against established CDC criteria demonstrated that 89% of subjects constituting Class 2 (well) were indeed nonfatigued controls. A general tendency for grouping CFS cases in the multiple symptomatic classes was noted.

CONCLUSION

This study established reasonably good validity for an empirically-derived latent class solution reflecting considerable heterogeneity among subjects with medically unexplained chronic fatigue. This work strengthens the growing understanding of CFS as a heterogeneous entity comprised of several conditions with different underlying pathophysiological mechanisms.

An empirical delineation of the heterogeneity of chronic unexplained fatigue in women

OBJECTIVES

To test the hypothesis that medically unexplained chronic fatigue and chronic fatigue syndrome (CFS) are heterogeneous conditions, and to define the different conditions using both symptom and laboratory data.

METHODS

We studied 159 women from KS, USA. A total of 51 of these suffered from fatigue consistent with established criteria for CFS, 55 had chronic fatigue of insufficient symptoms/severity for a CFS diagnosis and 53 were healthy controls matched by age and body mass index (BMI) against those with CFS. We used principal components analyses to define factors that best described the variable space and to reduce the number of variables. The 38 most explanatory variables were then used in latent class analyses to define discrete subject groups.

RESULTS

Principal components analyses defined six discrete factors that explained 40% of the variance. Latent class analyses provided several interpretable solutions with four, five and six classes. The four-class solution was statistically most convincing, but the six-class solution was more interpretable. Class 1 defined 41 (26%) subjects with obesity and relative sleep hypnoea. Class 2 were 38 (24%) healthy subjects. Class 3 captured 24 (15%) obese relatively hypnoeic subjects, but with low heart rate variability and cortisol. Class 4 were 23 (14%) sleep-disturbed and myalgic subjects without obesity or significant depression. The two remaining classes with 22 (14%) and 11 (7%) subjects consisted of the most symptomatic and depressed, but without obesity or hypnoea. Class 5 had normal sleep indices. Class 6 was characterized by disturbed sleep, with low sleep heart rate variability, cortisol, and sex hormones.

CONCLUSION

Chronic medically unexplained fatigue is heterogeneous. The putative syndromes were differentiated by obesity, sleep hypnoea, depression, physiological stress response, sleep disturbance, interoception and menopausal status. If these syndromes are externally validated and replicated, they may prove useful in determining the causes, pathophysiology and treatments of CFS.

Gene expression profile of empirically delineated classes of unexplained chronic fatigue

OBJECTIVES

To identify the underlying gene expression profiles of unexplained chronic fatigue subjects classified into five or six class solutions by principal component (PCA) and latent class analyses (LCA).

METHODS

Microarray expression data were available for 15,315 genes and 111 female subjects enrolled from a population-based study on chronic fatigue syndrome. Algorithms were developed to assign gene scores and threshold values that signified the contribution of each gene to discriminate the multiclasses in each LCA solution. Unsupervised dimensionality reduction was first used to remove noise or otherwise uninformative gene combinations, followed by supervised dimensionality reduction to isolate gene combinations that best separate the classes.

RESULTS

The authors' gene score and threshold algorithms identified 32 and 26 genes capable of discriminating the five and six multiclass solutions, respectively. Pair-wise comparisons suggested that some genes (zinc finger protein 350 [ZNF350], solute carrier family 1, member 6 [SLC1A6], F-box protein 7 [FBX07] and vacuole 14 protein homolog [VAC14]) distinguished most classes of fatigued subjects from healthy subjects, whereas others (patched homolog 2 [PTCH2] and T-cell leukemia/lymphoma [TCL1A]) differentiated specific fatigue classes.

CONCLUSION

A computational approach was developed for general use to identify discriminatory genes in any multiclass problem. Using this approach, differences in gene expression were found to discriminate some classes of unexplained chronic fatigue, particularly one termed interoception.

Chronic fatigue syndrome: the need for subtypes

Chronic fatigue syndrome (CFS) is an important condition confronting patients, clinicians, and researchers. This article provides information concerning the need for appropriate diagnosis of CFS subtypes. We first review findings suggesting that CFS is best conceptualized as a separate diagnostic entity rather than as part of a unitary model of functional somatic distress. Next, research involving the case definitions of CFS is reviewed. Findings suggest that whether a broad or more conservative case definition is employed, and whether clinic or community samples are recruited, these decisions will have a major influence in the types of patients selected. Review of further findings suggests that subtyping individuals with CFS on sociodemographic, functional disability, viral, immune, neuroendocrine, neurology, autonomic, and genetic biomarkers can provide clarification for researchers and clinicians who encounter CFS' characteristically confusing heterogeneous symptom profiles. Treatment studies that incorporate subtypes might be particularly helpful in better understanding the pathophysiology of CFS. This review suggests that there is a need for greater diagnostic clarity, and this might be accomplished by subgroups that integrate multiple variables including those in cognitive, emotional, and biological domains.