Symptom Clusters in Fibromyalgia: Potential Utility in Patient Assessment and Treatment Evaluation

A comparison of pain, fatigue, and function between post-COVID-19 condition, fibromyalgia, and chronic fatigue syndrome: a survey study

ABSTRACT

A growing number of individuals report prolonged symptoms following acute Coronavirus-19 (COVID-19) infection, known as post-COVID-19 condition (post-COVID-19). While studies have emerged investigating the symptom sequelae of post-COVID-19, there has been limited investigation into the characterization of pain, fatigue, and function in these individuals, despite initial reports of a clinical phenotype similar to fibromyalgia syndrome (FMS) and chronic fatigue syndrome (CFS)/myalgic encephalomyelitis (ME). This study aimed to characterize multiple symptom domains in individuals reporting post-COVID-19 and compare its clinical phenotype with those with FMS and CFS. A total of 707 individuals with a single or comorbid diagnosis of post-COVID-19, FMS, and/or CFS completed multiple surveys assessing self-reported pain, fatigue, physical and cognitive function, catastrophizing, kinesiophobia, anxiety, depression, dyspnea, and sleep quality. In all 3 diagnoses, elevated pain, fatigue, anxiety, depression, catastrophizing, and kinesiophobia were reported. Physical and cognitive function were similarly impacted among individuals with post-COVID-19, FMS, and CFS; however, individuals with post-COVID-19 reported lower pain and fatigue than FMS and CFS. The comorbid diagnosis of post-COVID-19 with FMS and/or CFS further exacerbated pain, fatigue, and psychological domains when compared with post-COVID-19 alone. In summary, individuals with post-COVID-19 report a symptom phenotype similar to FMS and CFS, negatively impacting cognitive and physical function, but with less severe pain and fatigue overall. These findings may help direct future investigations of the benefit of a biopsychosocial approach to the clinical management of post-COVID-19.

Distress as a mediator for pain and activities of daily living in older adults with fibromyalgia

Introduction

Pain, distress, and activities of daily living impact the lives of those with chronic pain. This study investigated distress (depressive symptoms, anxiety) on the relationship between pain (intensity and pain interference) and activities of daily living in individuals with fibromyalgia while controlling for age.

Methods

The current cross-sectional investigation focused on data from 123 men and women with fibromyalgia. Pain intensity, pain interference and anxiety were measured on 0-10 Likert type scales from the National Fibromyalgia Assessment Questionnaire. Depressive symptoms were assessed using the Beck Depression Inventory II. Activities of daily living (basic, instrumental) were measured with the Physical Activity Inventory Scale.

Results

It was hypothesized that the relationships between pain intensity and pain interference and activities of daily living in individuals with fibromyalgia would be mediated by the construct of distress while controlling for age. Mediation significantly occurred in both models as predicted. However, those who were older reported lower levels of pain intensity and distress than their younger counterparts, which may be related to time since diagnosis or other factors.

Discussion

Results of this study suggest that individuals with chronic pain conditions would benefit from treatment options which address distress, specifically depressive symptoms and anxiety.

Coping and Beliefs as Predictors of Functioning and Psychological Adjustment in Fibromyalgia Subgroups

Objectives

Research has pointed to two profiles of persons with fibromyalgia according to differences in functionality, thus distinguishing between functional and dysfunctional patients. The role of psychological factors underlying such clusters is unclear. This study aims to explore the contribution of pain beliefs and coping on fibromyalgia clustering.

Methods

A cluster analysis was performed to classify 238 women with fibromyalgia using the Fibromyalgia Impact Questionnaire and the Beck Depression Inventory as clustering variables. Cluster differences in physical functioning, depression, pain beliefs, coping, and age were then calculated (Student's t-test). Finally, a binary logistic regression was conducted to study the unique contribution of age, beliefs, and coping on cluster classification.

Results

Two clusters were revealed. Cluster 1 had a poor adaptation to fibromyalgia regarding physical functioning and depression. They generally embraced less adaptive beliefs (i.e., disability, harm, emotion, and requests) and coping strategies (i.e., guarding, resting, and asking for assistance). Cluster 2 showed a better adaptation to fibromyalgia and adopted more favorable beliefs (i.e., control) and coping strategies (i.e., exercise and task persistence). Cluster differences in age were significant but small. The backward binary logistic regression suggested a final model with six predictors (guarding, task persistence, harm, emotion, solicitude, and age) that explained 31% of the variance of group membership. Discussion. These results suggest that only a subset of psychological variables uniquely and independently contribute to functional/dysfunctional group membership. The results support the need to address psychological components in the management of fibromyalgia and point to a subset of preferred target beliefs and coping strategies.

Childhood and adult attention deficit hyperactivity disorder symptoms in fibromyalgia: associations with depression, anxiety and disease impact

Objective: The first aim of this study was to determine the prevalence of childhood and current attention deficit hyperactivity disorder (ADHD) symptoms in patients with fibromyalgia. The second aim is to assess the role of depression and anxiety on the relationship between childhood and adult ADHD symptoms with disease impact in this population.Methods: Sixty-four patients with fibromyalgia were compared to matched 58 healthy controls. All participants completed the Wender Utah Rating Scale (WURS), Adult ADHD Self-Report Scale (ASRS), Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI) and Fibromyalgia Impact Questionnaire (FIQ).Results: Patients with fibromyalgia had significantly higher mean scores of depression (BDI), anxiety (BAI), childhood ADHD symptoms (WURS) and adult ADHD symptoms (ASRS total, ASRS hyperactivity/impulsivity subscale and ASRS attention deficit subscale) than the control group. Fibromyalgia impact (FIQ) was significantly correlated with depression (BDI; r = 0.57, p < .001), anxiety (BAI; r = 0.56, p < .001) and childhood ADHD symptoms (WURS; r = 0.41, p < .001) in fibromyalgia group. There was no significant correlation between fibromyalgia impact (FIQ) and adult ADHD symptoms (ASRS total or sub-scale scores). Hierarchical multiple regression indicated that childhood ADHD symptoms (WURS), anxiety (BAI) and depression (BDI) predicted fibromyalgia impact. Both anxiety (BAI) and depression (BDI) mediated the relationship between childhood ADHD symptoms (WURS) and fibromyalgia impact (FIQ).Conclusion: Childhood ADHD symptoms may be a contributory factor to poorer functioning in the patients with fibromyalgia. The relationship was more pronounced in the presence of depression and anxiety symptoms. Evaluation of childhood and adult ADHD symptoms in patients with fibromyalgia is important for recognition and treatment of ADHD comorbidity and also for attenuating the severity of the disease.

An Empirically Derived Taxonomy of Biopsychosocial Factors of Adjustment to Fibromyalgia: Results of a Multivariate Analysis

Fibromyalgia (FM) is a lifelong central nervous system disorder that is precipitated by a range of biological, psycho-cognitive, and social factors. The aims of this exploratory study were to (a) identify biopsychosocial and cognitive factors that may affect an individual’s response to FM, (b) determine whether individuals with FM can be grouped into homogeneous subgroups based on biopsychosocial factors associated with response to FM, and (c) compare subgroup differences in health outcomes and life satisfaction. This study included 302 participants with FM. Principal components analysis yielded three sets of biopsychosocial factors that may affect response to FM (i.e., protective, cognitive-affective, and physical factors). Based on these three factors, a cluster analysis was performed, which produced three homogeneous subgroups: (a) the moderate amount of problems group, (b) the least amount of problems group, and (c) the many problems group. Analysis of variance (ANOVA) results indicated that these three subgroups differed significantly in terms of health outcomes and life satisfaction. The findings of this study broaden the existing literature related to understanding FM from a multidimensional symptom response perspective and contribute to the development and validation of biopsychosocial interventions for people with FM.

Somatic symptom presentations in women with fibromyalgia are differentially associated with elevated depression and anxiety

This study examined whether depression and anxiety differentially relate to fatigue, sleep disturbance, pain catastrophizing, fear of movement, and pain severity in women with fibromyalgia. Baseline data from the Fibromyalgia Activity Study with Transcutaneous Electrical Nerve Stimulation were analyzed. Of 191 participants, 50 percent reported high anxiety and/or depression (17% high anxiety, 9% high depression, and 24% both). Fatigue and sleep impairment were associated with high depression (p < 0.05). Pain severity, pain catastrophizing, and fear of movement were associated with high anxiety and high depression (p < 0.05). Possible implications for underlying mechanisms and the need for targeted treatments are discussed.

Fibromyalgia: A Critical and Comprehensive Review

Fibromyalgia is a disorder that is part of a spectrum of syndromes that lack precise classification. It is often considered as part of the global overview of functional somatic syndromes that are otherwise medically unexplained or part of a somatization disorder. Patients with fibromyalgia share symptoms with other functional somatic problems, including issues of myalgias, arthralgias, fatigue and sleep disturbances. Indeed, there is often diagnostic and classification overlap for the case definitions of a variety of somatization disorders. Fibromyalgia, however, is a critically important syndrome for physicians and scientists to be aware of. Patients should be taken very seriously and provided optimal care. Although inflammatory, infectious, and autoimmune disorders have all been ascribed to be etiological events in the development of fibromyalgia, there is very little data to support such a thesis. Many of these disorders are associated with depression and anxiety and may even be part of what has been sometimes called affected spectrum disorders. There is no evidence that physical trauma, i.e., automobile accidents, is associated with the development or exacerbation of fibromyalgia. Treatment should be placed on education, patient support, physical therapy, nutrition, and exercise, including the use of drugs that are approved for the treatment of fibromyalgia. Treatment should not include opiates and patients should not become poly pharmacies in which the treatment itself can lead to significant morbidities. Patients with fibromyalgia are living and not dying of this disorder and positive outlooks and family support are key elements in the management of patients.

Relation of dopamine receptor 2 binding to pain perception in female fibromyalgia patients with and without depression--A [¹¹C] raclopride PET-study

Dopamine D2/D3 receptor availability at rest and its association with individual pain perception was investigated using the [(11)C] raclopride PET-method in 24 female Fibromyalgia (FMS) participants with (FMS+, N=11) and without (FMS-, N=13) comorbid depression and in 17 healthy women. Thermal pain thresholds (TPT) and pain responses were assessed outside the scanner. We compared the discriminative capacity, i.e. the individual׳s capacity to discriminate between lower and higher pain intensities and the response criterion, i.e. the subject׳s tendency to report pain during noxious stimulation due to psychological factors. [(11)C] raclopride binding potential (BP), defined as the ratio of specifically bound non-displaceable radioligand at equilibrium (BP(ND)) was used as measure of D2/D3 receptor availability. We found significant group effects of BP(ND) in striatal regions (left ventral striatum, left caudate nucleus and left nucleus accumbens) between FMS+ and FMS- compared to healthy subjects. Correlational analysis showed negative associations between TPT and D2/D3 receptor availability in the left caudate nucleus in FMS-, between TPT and D2/D3 receptor availability in the right caudate nucleus in FMS + and positive associations between TPT and D2/D3 receptor availability in the left putamen and right caudate nucleus in healthy controls. The response criterion was positively associated with D2/D3 receptor availability in the right nucleus accumbens in FMS - and negatively with D2/D3 receptor availability in the left caudate nucleus in healthy controls. Finally, no significant associations between D2/D3 receptor availability and discriminative capacity in any of the groups or regions were determined. These findings provide further support for a disruption of dopaminergic neurotransmission in FMS and implicate DA as important neurochemical moderator of differences in pain perception in FMS patients with and without co-morbid depression.

Shared symptoms and putative biological mechanisms in chronic liver disease: implications for biobehavioral research

Liver disease affects over 25 million people in the United States and, despite advances in medical management resulting in increased survival, a majority of these individuals report multiple co-occurring symptoms that severely impair functioning and quality of life. The purpose of this review is to (1) propose defining these co-occurring symptoms as a symptom cluster of chronic liver disease (CLD), (2) discuss putative underlying biological mechanisms related to CLD, including the liver-gut-brain axis and influence of the microbiome, and (3) discuss the implications for biobehavioral research in this patient population. Biobehavioral research focusing on the interrelated, and possibly synergistic, mechanisms of these symptoms may lead to the development and testing of targeted symptom management interventions for improving function and quality of life in this growing patient population.

OMERACT-based fibromyalgia symptom subgroups: an exploratory cluster analysis

Introduction

The aim of this study was to identify subsets of patients with fibromyalgia with similar symptom profiles using the Outcome Measures in Rheumatology (OMERACT) core symptom domains.

Methods

Female patients with a diagnosis of fibromyalgia and currently meeting fibromyalgia research survey criteria completed the Brief Pain Inventory, the 30-item Profile of Mood States, the Medical Outcomes Sleep Scale, the Multidimensional Fatigue Inventory, the Multiple Ability Self-Report Questionnaire, the Fibromyalgia Impact Questionnaire–Revised (FIQ-R) and the Short Form-36 between 1 June 2011 and 31 October 2011. Hierarchical agglomerative clustering was used to identify subgroups of patients with similar symptom profiles. To validate the results from this sample, hierarchical agglomerative clustering was repeated in an external sample of female patients with fibromyalgia with similar inclusion criteria.

Results

A total of 581 females with a mean age of 55.1 (range, 20.1 to 90.2) years were included. A four-cluster solution best fit the data, and each clustering variable differed significantly (P <0.0001) among the four clusters. The four clusters divided the sample into severity levels: Cluster 1 reflects the lowest average levels across all symptoms, and cluster 4 reflects the highest average levels. Clusters 2 and 3 capture moderate symptoms levels. Clusters 2 and 3 differed mainly in profiles of anxiety and depression, with Cluster 2 having lower levels of depression and anxiety than Cluster 3, despite higher levels of pain. The results of the cluster analysis of the external sample (n = 478) looked very similar to those found in the original cluster analysis, except for a slight difference in sleep problems. This was despite having patients in the validation sample who were significantly younger (P <0.0001) and had more severe symptoms (higher FIQ-R total scores (P = 0.0004)).

Conclusions

In our study, we incorporated core OMERACT symptom domains, which allowed for clustering based on a comprehensive symptom profile. Although our exploratory cluster solution needs confirmation in a longitudinal study, this approach could provide a rationale to support the study of individualized clinical evaluation and intervention.

Sleep disturbances of adult women suffering from fibromyalgia: a systematic review of observational studies

Although sleep complaints are often reported in patients with fibromyalgia syndrome (FMS), there is no conclusive evidence that these complaints represent symptomatic disorders of sleep physiology. Thus, the question of the role of sleep disturbances as an etiological or maintenance factor in FMS remains open. This study identifies the subjective and objective characteristics of sleep disturbances in adult women diagnosed with FMS. We carried out a systematic review of publications since 1990, the publication year of the American College of Rheumatology criteria of FMS. We selected empirical studies comparing sleep characteristics of adult women with FMS and healthy women or women with rheumatic diseases. We identified 42 articles. Patients with FMS were more likely to exhibit sleep complaints and also a less efficient, lighter and fragmented sleep. The evidence of a FMS signature on objective measures of sleep is inconsistent, however, as the majority of studies lacks statistical power. Current evidence cannot confirm the role played by sleep physiology in the pathogenesis or maintenance of FMS symptoms; nonetheless, it is clear that sleep disturbances are present in this syndrome.

Cluster analysis of clinical data identifies fibromyalgia subgroups

INTRODUCTION

Fibromyalgia (FM) is mainly characterized by widespread pain and multiple accompanying symptoms, which hinder FM assessment and management. In order to reduce FM heterogeneity we classified clinical data into simplified dimensions that were used to define FM subgroups.

MATERIAL AND METHODS

48 variables were evaluated in 1,446 Spanish FM cases fulfilling 1990 ACR FM criteria. A partitioning analysis was performed to find groups of variables similar to each other. Similarities between variables were identified and the variables were grouped into dimensions. This was performed in a subset of 559 patients, and cross-validated in the remaining 887 patients. For each sample and dimension, a composite index was obtained based on the weights of the variables included in the dimension. Finally, a clustering procedure was applied to the indexes, resulting in FM subgroups.

RESULTS

VARIABLES CLUSTERED INTO THREE INDEPENDENT DIMENSIONS: "symptomatology", "comorbidities" and "clinical scales". Only the two first dimensions were considered for the construction of FM subgroups. Resulting scores classified FM samples into three subgroups: low symptomatology and comorbidities (Cluster 1), high symptomatology and comorbidities (Cluster 2), and high symptomatology but low comorbidities (Cluster 3), showing differences in measures of disease severity.

CONCLUSIONS

We have identified three subgroups of FM samples in a large cohort of FM by clustering clinical data. Our analysis stresses the importance of family and personal history of FM comorbidities. Also, the resulting patient clusters could indicate different forms of the disease, relevant to future research, and might have an impact on clinical assessment.

Chronic pain and the development of a symptom checklist: a pilot study

BACKGROUND

There is currently no instrument to systematically assess the range of symptoms/problems and their bothersomeness in patients with chronic non-cancer pain (CNPN). Systematic assessment and prioritizing may target treatments and improve outcomes.

METHODS

The authors developed a checklist of symptoms and problems, the Copenhagen Symptom Checklist (CSC), presented clinically by patients. Fifty-three items representing biological, psychological and social areas were selected. Symptom/problem severity was rated on a 5-point scale anchored at 0 = 'not at all' and 4 = 'severe'. Patients ranked the five most bothersome symptoms/problems and could add five open-ended items. Patients completed the CSC after the first visit at the multidisciplinary pain centre.

RESULTS

One hundred and twelve consecutive patients completed the CSC. Eighty-nine percent scored pain as rather severe or very severe (score = 3 plus score = 4), followed by reduction in physical activity (67%), fatigue (66%) and sleep disturbance (53%). Pain and fatigue, but not reduction in physical activity, were given highest priority. Cognitive problems were important to a third of the patients. Depressive symptoms, cognitive problems and worry explained 17.5% of the total variance. Patients filled in the CSC without important loss of information, but a minority prioritized more than three areas or used the free text alternative.

CONCLUSIONS

Patients prioritized pain and fatigue as the most burdensome symptoms, but reduction in physical activity and sleep problems were also highly ranked. Patients were positive to the idea of symptom reporting; however, the 53-item number in this version of CSC is larger than may be necessary.

Cognitive performance in women aged 50 years and older with and without fibromyalgia

OBJECTIVES

Persons with fibromyalgia (FM) report having cognitive dysfunction. Neuropsychological performance was compared across a variety of domains in 43 women with FM (Mage = 63 years) and in 44 women without FM (Mage = 65 years).

METHOD

Measures included explicit memory (Consortium to Establish a Registry for Alzheimer's Disease [CERAD] immediate/delayed recall, delayed recognition), aspects of executive function including interference/inhibition (Stroop Color/Word test), working memory (Digit Span Forward/Backward), set-shifting/complex sequencing (Trails B), monitoring (verbal fluency: naming animals), processing speed (Trails A, Digit Symbol Substitution Coding), and problem solving (Everyday Problems Test).

RESULTS

Women with FM performed more poorly than controls on executive function (Stroop Color/Word) and one processing speed measure (Digit Symbol Substitution Coding).

DISCUSSION

Results partly support altered cognitive function in FM. Mixed findings across cognitive domains among individuals with or without FM is consistent with the literature and suggest that factors beyond those typically controlled for (e.g., heterogeneity in FM) may be influencing findings. Future research is warranted.

Information seeking over the course of illness: the experience of people with fibromyalgia

OBJECTIVE

Although there is literature addressing the fibromyalgia illness experience, there has been limited work concerning how people with fibromyalgia utilize health information. The aim of this study was therefore to investigate the information needs and information-seeking patterns of such individuals, and how these might change over time.

METHODS

Data were collected through an online survey of fibromyalgia-related information behaviours (N = 190). The participants were recruited through two methods: an email invitation sent out over a university listserv including faculty, staff and students, and invitational posts on fibromyalgia discussion boards on various health-related websites.

RESULTS

Respondents used the internet most frequently, but also placed great value on information from others, including healthcare practitioners, family and friends. Among the online sources, organization websites, health portals and health-related social networking sites were most frequently used. Topics of interest to people with fibromyalgia vary as they move from an initial stage of confusion, to diagnosis and eventually to a stage of equilibrium in which they are satisfied with their management of their condition. Aside from symptoms and treatments, topics often reflect a need to understand the meaning of their condition and coping skills.

CONCLUSION

The areas of information need identified in the present study can be used to tailor patient education materials and information services to address contextual and temporal factors in the illness experiences of those with fibromyalgia.

Exploring online support spaces: using cluster analysis to examine breast cancer, diabetes and fibromyalgia support groups

OBJECTIVE

This study sought to characterize and compare online discussion forums for three conditions: breast cancer, type 1 diabetes and fibromyalgia. Though there has been considerable work examining online support groups, few studies have considered differences in discussion content between health conditions. In addition, in contrast to the extant literature, this study sought to employ a semi-automated approach to examine health-related online communities.

METHODS

Online discussion content for the three conditions was compiled, pre-processed, and clustered at the thread level using the bisecting k-means algorithm.

RESULTS

Though the clusters for each condition differed, the clusters fell into a set of common categories: Generic, Support, Patient-Centered, Experiential Knowledge, Treatments/Procedures, Medications, and Condition Management.

CONCLUSION

The cluster analyses facilitate an increased understanding of various aspects of patient experience, including significant emotional and temporal aspects of the illness experience.

PRACTICE IMPLICATIONS

The clusters highlighted the changing nature of patients' information needs. Information provided to patients should be tailored to address their needs at various points during their illness. In addition, cluster analysis may be integrated into online support groups or other types of online interventions to assist patients in finding information.

Clinical dimensions of fibromyalgia symptoms and development of a combined index of severity: the CODI index

BACKGROUND

Although a large body of work indicates that fibromyalgia (FM) is not a discrete entity, few studies have attempted to classify the heterogeneity of FM symptoms. The objectives of the present study were to confirm the existence of two latent dimensions underlying FM symptoms (Core-FM symptoms and Distress) by means of factor analysis techniques, and to develop and validate a new combined index of symptom severity (the CODI).

METHODS

We analyzed and combined the baseline scores on six visual analog scales of the FIQ (pain, general fatigue, morning fatigue, stiffness, anxiety, and depression) and on the STAI-T (trait anxiety) of 216 Spanish patients diagnosed with FM (97.7% women) who were participating in a randomized, controlled trial.

RESULTS

The principal component analysis indicated the presence of two correlated factors (labeled as Core-FM symptoms and Distress) that explained 64% of total variance. The subsequent confirmatory factor analysis yielded more empirical support for the two-factor model than the one-factor model (all items loading on one latent dimension). The two factors possessed adequate internal consistency and construct validity given the pattern of significant correlations with the Euroqol items. The Core-FM dimension had a stronger relationship with mobility, self-care, usual activities, and pain/discomfort than with anxiety/depression, whereas the Distress dimension showed the opposite pattern. Finally, summing the standardized scores of the two dimensions, a new combined index of symptom severity (the CODI) was developed.

CONCLUSION

The clinical implications and utility of the CODI are discussed in relation to previous research on FM.

Association of employment and working conditions with physical and mental health symptoms for people with fibromyalgia

PURPOSE

This study examines physical and mental health symptoms among people with fibromyalgia (FM) by employment status and working conditions.

METHOD

Secondary data analysis of the 2007 National Fibromyalgia Association Questionnaire study resulted in employment and symptom information for 1702 people of working age with FM. In this cross-sectional internet study, six factors of symptom clusters (physical, mental health, sleeping, concentration, musculoskeletal, support) were seen in the data. Linear regression models used employment, age, income, gender, and education to predict symptom clusters. Among those employed, working conditions were also associated with symptom severity.

RESULTS

In the predominately female sample, 51% were working. Of these, 70% worked over 30 hours/week and half had flexible hours. Employment, higher income, and education were strongly associated with fewer symptoms. Working conditions, including level of physical and mental exertion required on the job as well as coworkers' understanding of FM, were related to symptoms, particularly physical and mental health symptoms. Many participants reported modifying their work environment (66%) or changing occupations (33%) due to FM.

CONCLUSIONS

Work modifications could allow more people with FM to remain employed and alleviate symptoms. Persons with FM should be counseled to consider what elements of their work may lead to symptom exacerbation.

Identification of symptom and functional domains that fibromyalgia patients would like to see improved: a cluster analysis

BACKGROUND

The purpose of this study was to determine whether some of the clinical features of fibromyalgia (FM) that patients would like to see improved aggregate into definable clusters.

METHODS

Seven hundred and eighty-eight patients with clinically confirmed FM and baseline pain > or =40 mm on a 100 mm visual analogue scale ranked 5 FM clinical features that the subjects would most like to see improved after treatment (one for each priority quintile) from a list of 20 developed during focus groups. For each subject, clinical features were transformed into vectors with rankings assigned values 1-5 (lowest to highest ranking). Logistic analysis was used to create a distance matrix and hierarchical cluster analysis was applied to identify cluster structure. The frequency of cluster selection was determined, and cluster importance was ranked using cluster scores derived from rankings of the clinical features. Multidimensional scaling was used to visualize and conceptualize cluster relationships.

RESULTS

Six clinical features clusters were identified and named based on their key characteristics. In order of selection frequency, the clusters were Pain (90%; 4 clinical features), Fatigue (89%; 4 clinical features), Domestic (42%; 4 clinical features), Impairment (29%; 3 functions), Affective (21%; 3 clinical features), and Social (9%; 2 functional). The "Pain Cluster" was ranked of greatest importance by 54% of subjects, followed by Fatigue, which was given the highest ranking by 28% of subjects. Multidimensional scaling mapped these clusters to two dimensions: Status (bounded by Physical and Emotional domains), and Setting (bounded by Individual and Group interactions).

CONCLUSION

Common clinical features of FM could be grouped into 6 clusters (Pain, Fatigue, Domestic, Impairment, Affective, and Social) based on patient perception of relevance to treatment. Furthermore, these 6 clusters could be charted in the 2 dimensions of Status and Setting, thus providing a unique perspective for interpretation of FM symptomatology.

Symptom clusters: myth or reality?

Clinical experience suggests that many symptoms occur together. In this paper, we examine the rationale and evidence base for symptom clusters in different medical fields, particularly the cluster phenomenon in cancer. Cancer symptom clusters are a reality. Various symptoms that cluster clinically have also been verified statistically. Specific clusters such as nausea-vomiting, anxiety-depression, and cough-dyspnea are evident on both clinical observation and in research investigation. Fatigue-pain and fatigue-insomnia-pain have also been demonstrated statistically as clusters. Another proposed cluster 'depression-fatigue-pain' seems relevant to clinical practice. Other clusters may serve only as theoretical models that illustrate possible common biological etiologies in cancer; they need to be validated in future research. Analysis of the literature is complicated by considerable inconsistencies across studies. Discrepancies between clinically defined and statistically obtained clusters raise important questions. We must consider the analytical techniques used, and how methodology might influence cluster occurrence and composition. Further research is warranted to establish universally accepted statistical methods and assessment tools for symptom cluster research.