The way forward: a case for longitudinal population-based studies in the field of functional somatic syndromes

Connecting the dots: Network structures of internalizing and functional symptoms in a population-based cohort

OBJECTIVE

Comorbidities between internalizing disorders (IDs) and functional disorders (FDs) are well-documented, indicating shared pathways. However, their symptom-level relationships have been largely unexplored. This exploratory study employs a network approach to investigate symptoms of major depressive disorder (MDD), generalized anxiety disorder (GAD), myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), fibromyalgia (FM), and irritable bowel syndrome (IBS) to identify bridge symptoms explaining comorbidity between the two domains.

METHODS

We used cross-sectional data on 72,919 adult subjects from the Lifelines Cohort Study, a Dutch general population sample. A total of 38 symptoms representing diagnostic criteria of IDs and FDs were assessed with validated questionnaires. Network models were estimated using eLasso, based on the Ising model, to identify bridge symptoms. The Network Comparison Test (NCT) was used to test whether there were differences in network structure and strength across sex and age.

RESULTS

Symptoms were moderately connected, with a network density of 52.7%. ID and FD symptoms clustered in their respective domains, but were connected through the bridge symptoms, fatigue, difficulty concentrating, trouble sleeping, and unrefreshing sleep. Fatigue and difficulty concentrating had the most connections, associated with 86.6% and 78.9% of the other symptoms, respectively. NCTs indicated no differences in network connectivity between females versus males or younger versus older adults (>50 years).

CONCLUSIONS

ID and FD symptoms are moderately interconnected. Bridge symptoms displaying strong connections to multiple disorders may play a central role in the mechanisms underpinning the comorbidity between IDs and FDs.

Comorbidity and sex differences in functional disorders and internalizing disorders

OBJECTIVE

In the current exploratory study we estimate comorbidity rates between FDs [fibromyalgia (FM), myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), and irritable bowel syndrome (IBS)]-and IDs-[major depressive disorder (MDD) and generalized anxiety disorder (GAD)] by using self-reported diagnostic criteria.

METHOD

We analyzed data from 107,849 participants (mean age = 49.3 (SD = 13.0), 58.6% women) of the Lifelines Cohort Study. Lifelines is a prospective population-based cohort study in the northeast of the Netherlands. Current IDs were assessed using the Mini-International Neuropsychiatric Interview. Current FM, ME/CFS, and IBS were assessed according to the 2010 American College of Rheumatology criteria, the 1994 Centers for Disease Control and Prevention criteria and the ROME IV criteria, respectively. We estimated tetrachoric correlations between diagnoses and tested for sex differences. Additionally, we estimated the ratio of observed-to-expected frequency for combinations of diagnoses.

RESULTS

FDs and IDs are highly comorbid (odds ratios: 3.2-12.6) with associations stronger among men. Participants with at least three disorders/diagnoses were more prevalent than expected by chance.

CONCLUSION

Studies that aim to explain sex differences and the comorbidity of specific combinations of IDs and FDs will be an important contribution to understanding the etiology of these conditions.

Aetiological Understanding of Fibromyalgia, Irritable Bowel Syndrome, Chronic Fatigue Syndrome and Classificatory Analogues: A Systematic Umbrella Review

Background

This umbrella review systematically assesses the variety and relative dominance of current aetiological views within the scientific literature for the three most investigated symptom-defined functional somatic syndromes (FSS) and their classificatory analogues within psychiatry and psychology.

Method

An umbrella review of narrative and systematic reviews with and without meta-analyses based on a search of electronic databases (PubMed, Web of Science, Embase, PsychINFO) was conducted. Eligible reviews were published in English, focused on research of any kind of aetiological factors in adults diagnosed with fibromyalgia syndrome (FMS), irritable bowel syndrome (IBS), chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME), and somatic symptom disorder (SSD)/somatoform disorder (SFD).

Results

We included 452 reviews (132 systematic reviews including meta-analyses, 133 systematic reviews, 197 narrative reviews), of which 132 (29%) focused on two or more of the investigated health conditions simultaneously. Across diagnoses, biological factors were addressed in 90% (k = 405), psychological in 33% (k = 150), social in 12% (k = 54), and healthcare factors in 5% (k = 23) of the reviews. The methodological quality of the included systematic reviews (k = 255) was low (low/critically low: 41% [k = 104]; moderate: 49% [k = 126]; high quality: 10% [k = 25]). The high-quality systematic reviews suggest that deficient conditioned pain modulation, genetic factors, changes in the immune, endocrinological, gastrointestinal, cardiovascular, and nervous system, and psychosocial factors such as sexual abuse and pain catastrophizing increase the risk for FSS.

Conclusion

Only very few systematic reviews have used comprehensive, biopsychosocial disease models to guide the selection of aetiological factors in FSS research. Future research should strive for higher scientific standards and broaden its perspective on these health conditions.

Examine the public health impacts of functional somatic disorders using the DanFunD study

Background: Persistent physical symptoms (e.g. pain, fatigue) are prevalent in the population and some persons may develop a functional somatic disorder (FSD). We still need to explore the limits between general bodily sensations and FSD, and great controversies exist as regard delimitation, occurrence, risk factors, prognosis, and costs of FSD in the general population. This is mainly due to the lack of focused, sufficient powered, population-based epidemiological studies. Material and Methods: The DanFunD study is the largest focused population-based study on FSD and has the potential to answer these crucial questions regarding the FSD disorders. DanFunD has its origin in the Copenhagen area of Denmark and was initiated in 2009 by an interdisciplinary team of researchers including basic scientists, clinical researchers, epidemiologists, and public health researchers. A population-based cohort of nearly 10,000 people have filled in detailed questionnaires, gone through a thorough health examination, and a biobank is established. The cohort was re-examined after five years. Results:The prevalence of FSD in the Danish population is about 10-15% and is twice as common in women as in men. Persons with FSD report impaired daily activities and low self-perceived health, which qualifies FSD as a major public health problem. The research plan to unravel the risk factors for FSD employs a bio-psycho-social approach according to a detailed plan. Preliminary results are presented, and work is in progress. Likewise, plans for assessing prognosis and health care costs are provided. Conclusion: We invite researchers in the field to collaborate on this unique data material.

Irritable bowel, chronic widespread pain, chronic fatigue and related syndromes are prevalent and highly overlapping in the general population: DanFunD

Prevalence of functional somatic syndromes (FSS) in the general population varies with observed overlap between syndromes. However, studies including a range of FSS are sparse. We investigated prevalence and characteristics of various FSS and the unifying diagnostic construct bodily distress syndrome (BDS), and identified mutual overlap of the FSS and their overlap with BDS. We included a stratified subsample of 1590 adults from a randomly selected Danish general population sample (n = 7493). Telephonic diagnostic interviews performed by three trained physicians were used to identify individuals with FSS and BDS. Prevalence of overall FSS was 9.3%; 3.8% for irritable bowel, 2.2% for chronic widespread pain, 6.1% for chronic fatigue, 1.5% for whiplash associated disorders, and 0.9% for multiple chemical sensitivity. Prevalence of BDS was 10.7% where 2.0% had the multi-organ type. FSS were highly overlapping with low likelihood of having a “pure” type. Diagnostic agreement of FSS and BDS was 92.0%. Multi-syndromatic FSS and multi-organ BDS were associated with female sex, poor health, physical limitations, and comorbidity. FSS are highly prevalent and overlapping, and multi-syndromatic cases are most affected. BDS captured the majority of FSS and may improve clinical management, making the distinction between multi- and mono-syndromatic patients easier.

A step towards a new delimitation of functional somatic syndromes: A latent class analysis of symptoms in a population-based cohort study

OBJECTIVES

The current delimitation of functional somatic syndromes (FSS) is inconsistent. We aimed to investigate somatic symptom profiles in the general adult population to contribute to a new, data-driven delimitation of FSS.

METHODS

Information on 31 self-reported somatic symptoms used in the delimitation of various FSS and bodily distress syndrome (BDS) was obtained from the DanFunD study-a population-based cohort study on 9656 adults (participation 33.6%) from Greater Copenhagen, Denmark. Latent class analysis was used to identify symptom profiles. The profiles were described by their relation with sex, age, chronic disease, self-perceived health, symptom impact, self-reported FSS, and BDS case-status.

RESULTS

Eight symptom profiles were identified. The largest profile had no symptoms (49% of the population). Three profiles were characterized by a few, specific symptoms: muscle and joint pain (17%), gastrointestinal symptoms (6%), and general symptoms (13%). Three profiles had multiple symptoms in specific combinations: musculoskeletal and general symptoms (7%); fatigue, musculoskeletal and gastrointestinal symptoms (3%); and cardiopulmonary, gastrointestinal and general symptoms (3%). Lastly, one profile (2%) had high probability of all symptoms. The last four profiles (15%) were strongly associated with BDS case-status, poor self-perceived health and high impact of symptoms. Analyses excluding persons with multi-symptomatic chronic disease showed similar results.

CONCLUSIONS

We identified eight symptom profiles characterized by specific combinations of symptoms. Four of these had multiple symptoms from several bodily systems showing large overlap with BDS, possibly indicating subtypes of FSS. The profiles contribute to a new delimitation of FSS by illustrating the importance of specific symptom combinations.

Cohort description: The Danish study of Functional Disorders

The Danish study of Functional Disorders (DanFunD) cohort was initiated to outline the epidemiology of functional somatic syndromes (FSS) and is the first larger coordinated epidemiological study focusing exclusively on FSS. FSS are prevalent in all medical settings and can be defined as syndromes that, after appropriate medical assessment, cannot be explained in terms of a conventional medical or surgical disease. FSS are frequent and the clinical importance varies from vague symptoms to extreme disability. No well-described medical explanations exist for FSS, and how to delimit FSS remains a controversial topic. The specific aims with the cohort were to test delimitations of FSS, estimate prevalence and incidence rates, identify risk factors, delimitate the pathogenic pathways, and explore the consequences of FSS. The study population comprises a random sample of 9,656 men and women aged 18–76 years from the general population examined from 2011 to 2015. The survey comprises screening questionnaires for five types of FSS, ie, fibromyalgia, whiplash-associated disorder, multiple chemical sensitivity, irritable bowel syndrome, and chronic fatigue syndrome, and for the unifying diagnostic category of bodily distress syndrome. Additional data included a telephone-based diagnostic interview assessment for FSS, questionnaires on physical and mental health, personality traits, lifestyle, use of health care services and social factors, and a physical examination with measures of cardiorespiratory and morphological fitness, metabolic fitness, neck mobility, heart rate variability, and pain sensitivity. A biobank including serum, plasma, urine, DNA, and microbiome has been established, and central registry data from both responders and nonresponders are similarly available on morbidity, mortality, reimbursement of medicine, heath care use, and social factors. A complete 5-year follow-up is scheduled to take place from year 2017 to 2020, and further reexaminations will be planned. Several projects using the DanFunD data are ongoing, and findings will be published in the coming years.

Age- and sex-specific associations between adverse life events and functional bodily symptoms in the general population

OBJECTIVE

To test age- and sex-specific associations between adverse life events and functional bodily symptoms (FBS) in the general population.

METHODS

In a population-based cohort, 964 participants (mean age 55 years SD 11, 48% male) completed two measurements waves of the present study. Lifetime exposure to 12 adverse life events was assessed through a modified version of the List of Threatening Experiences. Stress-sensitive personality was assessed with the 12-item neuroticism scale of the Eysenck Personality Questionnaire-Revised. Socio-economic status was retrieved from questionnaires. Participants completed the somatization section of the Composite International Diagnostic Interview to survey the presence of 42 FBS in the previous year.

RESULTS

Regression analyses, adjusted for age, revealed that lifetime scores of adverse life events were significantly associated with FBS in the previous year, an association that was nearly identical for females (beta=0.18, t=4.07, p<0.01) and males (beta=0.19, t=4.24, p<0.01). This association remained statistically significant when stress-sensitive personality and socio-economic status were added to the model. Associations between adverse life events during childhood and FBS were statistically significant in females (beta=0.13, t=2.90, p=0.04) but not in males (beta=0.06, t=1.24, p=0.22), whereas there was a stronger association with adverse life events during adulthood in males (beta=0.20, t=4.37, p<0.01) compared to females (beta=0.15, t=3.38, p=0.01). Life events in the previous year were not associated with FBS in the previous year.

CONCLUSION

Adverse life events during lifetime were associated with FBS in the previous year. This association was dependent on age and sex but largely independent of having a stress-sensitive personality or low socio-economic status. Future studies could adopt a life course perspective to study the role of adverse life events in FBS.

In search of risk factors for chronic pain in adolescents: a case-control study of childhood and parental associations

Objectives

This study was designed to investigate whether an individual and parental history of functional pain syndromes (FPS) is found more often in adolescents suffering from chronic pain than in their pain-free peers.

Methods

Our case–control study involved 101 adolescents aged 10–18 years. Cases were 45 patients of the Chronic Pain Clinic at Sydney Children’s Hospital with diverse chronic pain disorders. Controls consisted of 56 adolescent volunteers who did not have chronic pain. Adolescents and their parents filled out questionnaires assessing demographic data as well as known and potential risk factors for chronic pain. A history of FPS was assessed by questionnaire, including restless legs syndrome (RLS). Chi-squared tests and t-tests were used to investigate univariate associations between chronic pain in adolescents and lifetime prevalence of FPS. Logistic regression was used to test multivariate associations, while controlling for possible confounders.

Results

Migraine, non-migraine headaches, recurrent abdominal pain (RAP), and RLS were reported significantly more frequently in cases than controls (P-values of 0.01, <0.001, 0.01, and 0.03, respectively). Parental migraine, RAP, and RLS were also significantly associated with adolescent chronic pain in the multivariate analyses. Individual history of migraine, non-migraine headaches, and RAP, along with parental history of RAP and depression significantly accounted for 36%–49% of variance in chronic pain. Other associations with chronic pain were generally in accordance with previous reports.

Discussion

It may be helpful when assessing a child who has chronic pain or is at risk of chronic pain, to enquire about these associations. Based on the current findings, an individual history of migraine, non-migraine headaches, and RAP, as well as parental migraine, RAP, and RLS are symptoms that are of particular relevance to assess.

How to assess common somatic symptoms in large-scale studies: a systematic review of questionnaires

OBJECTIVE

Many questionnaires for assessment of common somatic symptoms or functional somatic symptoms are available and their use differs greatly among studies. The prevalence and incidence of symptoms are partially determined by the methods used to assess them. As a result, comparison across studies is difficult. This article describes a systematic review of self-report questionnaires for somatic symptoms for use in large-scale studies and recommends two questionnaires for use in such studies.

METHODS

A literature search was performed in the databases Medline, PsycINFO and EMBASE. Articles that reported the development, evaluation, or review of a self-report somatic symptom measure were included. Instrument evaluation was based on validity and reliability, and their fitness for purpose in large scale studies, according to the PhenX criteria.

RESULTS

The literature search identified 40 questionnaires. The number of items within the questionnaires ranged from 5 to 78 items. In 70% of the questionnaires, headaches were included, followed by nausea/upset stomach (65%), shortness of breath/breathing trouble (58%), dizziness (55%), and (low) back pain/backaches (55%). Data on validity and reliability were reported and used for evaluation.

CONCLUSION

Questionnaires varied regarding usability and burden to participants, and relevance to a variety of populations and regions. Based on our criteria, the Patient Health Questionnaire-15 and the Symptom Checklist-90 somatization scale seem the most fit for purpose for use in large-scale studies. These two questionnaires have well-established psychometric properties, contain relevant symptoms, are relatively short, and are available in multiple languages.

Prevalence of somatoform disorders and medically unexplained symptoms in old age populations in comparison with younger age groups: a systematic review

OBJECTIVE

To review current knowledge regarding the prevalence of somatization problems in later life by level of caseness (somatoform disorders and medically unexplained symptoms, MUS) and to compare these rates with those in middle-aged and younger age groups.

METHOD

A systematic search of the literature published from 1966 onwards was conducted in the Pubmed and EMBASE databases.

RESULTS

Overall 8 articles, describing a total of 7 cohorts, provided data of at least one prevalence rate for somatoform disorders or MUS for the middle-aged (50-65 years) or older age (≥65 years) group. Prevalence rates for somatoform disorders in the general population range from 11 to 21% in younger, 10 to 20% in the middle-aged, and 1.5 to 13% in the older age groups. Prevalence rates for MUS show wider ranges, of respectively 1.6-70%, 2.4-87%, and 4.6-18%, in the younger, middle, and older age groups, which could be explained by the use of different instruments as well as lack of consensus in defining MUS.

CONCLUSION

Somatoform disorders and MUS are common in later life, although the available data suggest that prevalence rates decline after the age of 65 years. More systematic research with special focus on the older population is needed to understand this age-related decline in prevalence rates.

Annual research review: functional somatic symptoms and associated anxiety and depression--developmental psychopathology in pediatric practice

BACKGROUND

Medically unexplained physical symptoms, commonly referred to as functional somatic symptoms (FSS), are common in pediatric medical settings and associated with suffering, impairment, and medical help seeking. The association of pediatric FSS with anxiety and depressive symptoms and disorders across the life span is reviewed.

METHOD

Review and critique of controlled studies examining cross-sectional and longitudinal associations of FSS with anxiety and depressive symptoms and disorders in community-based and clinical samples of children and adolescents.

RESULTS

FSS are consistently associated cross-sectionally with anxiety and depressive symptoms and disorders in childhood and adolescence, and the likelihood of associated anxiety and depression increases with the number of reported FSS. The presence of one or more FSS early in life is associated with an increased likelihood of multiple FSS and anxiety and depressive symptoms and disorders later in life, and anxiety and depressive symptoms and disorders in childhood are associated with subsequent multiple FSS.

CONCLUSION

Strong associations between FSS, anxiety, and depression across the life span suggest the need to reconsider existing nosology and reconceptualize symptomatic relationships. Large, population-based longitudinal studies of FSS, anxiety, and depressive symptoms and disorders are needed to establish temporal relationships between the various symptoms and conditions.

Meta-analysis and meta-regression of hypothalamic-pituitary-adrenal axis activity in functional somatic disorders

Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis is the most investigated biological risk marker in functional somatic disorders (FSDs), such as chronic fatigue syndrome (CFS), fibromyalgia (FM), and irritable bowel syndrome (IBS). Our aim was to assess whether there is an association between basal hypocortisolism and FSD and to identify potential moderators of this association. Meta-analysis on 85 studies revealed that although basal cortisol levels were generally lower in FSD subjects compared to controls, this association did not reach statistical significance (SMD -0.07, 95% CI -0.17 to 0.04, p=0.241). However, when the three FSD were assessed separately, statistically significant basal hypocortisolism was observed in CFS subjects compared to controls (SMD -0.14, 95% CI -0.28 to 0.00, p=0.047), but not in FM or IBS. When all potential moderators were entered into a meta-regression analysis, only type of FSD and female gender were significant independent predictors of basal hypocortisolism. In conclusion, we did not find evidence to consider all three main FSD as hypocortisolemic disorders, as significant reduction in basal cortisol compared to healthy controls was only found in CFS and in females with FM, but not in IBS.