| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
SOMATIC PRESENTATIONS: EPIDEMIOLOGY |
From King's College London (R.A.A.K., S.C.W.), Department of Psychological Medicine, Institute of Psychiatry, London, UK; Université Paris Descartes (J.P.L.), Faculté de Pharmacie, Neuropsychopharmacologie des Addictions, CNRS, et Université Paris 7, France; INSERM (J.P.L.), Paris, France; Assistance Publique-Hôpitaux de Paris (J.P.L.), Hôpital Fernand Widal, Service de Psychiatrie, Paris, France.
Address correspondence and reprint requests to Simon Wessely, Institute of Psychiatry, Department of Psychological Medicine, P062, Weston Education Centre, London SE5 9RJ, UK. E-mail: s.wessely{at}iop.kcl.ac.uk
ABSTRACT
Objective: To review the evidence for overlap in the phenomenology of the Functional Somatic Syndromes (FSS). The FSS show considerable comorbidity, leading some to suggest they may be aspects of the same disorder.
Methods: We conducted a selective review of peer-reviewed articles on the co-occurrence of FSS symptoms and diagnoses.
Results: Considerable evidence of overlap was found at the level of symptoms, diagnostic criteria, and clinical diagnoses made.
Conclusions: Phenomenological commonalities support a close relationship between the FSS, although differences remain in other domains. Whether the FSS may best be considered the same or different will depend on the pragmatics of diagnosis.
Key Words: diagnosis • chronic fatigue syndrome • irritable bowel syndrome • fibromyalgia • phenomenology • comorbidity
Abbreviations: IBS = irritable bowel syndrome; FSS = functional somatic syndromes; DSM = Diagnostic and Statistical Manual; CFS = chronic fatigue syndrome; FM = fibromyalgia; OR = odds ratio.
INTRODUCTION
Somatic symptoms without a clear medical explanation are common in the community and in medical settings (1–4). Many people report more than one such symptom (3,5), and these multiple symptoms are sometimes grouped together as the various "Functional Somatic Syndromes" (FSS). Of itself, this term tells us nothing about etiology—in particular, there is no implication that these symptoms arise through the hypothetical process of somatization. Simply put, these are clusters of physical symptoms occurring together for which no adequate medical explanation has been found, and which doctors have grouped into syndromes. There is a long and changing list of these FSS, which currently includes chronic fatigue syndrome, irritable bowel syndrome, and multiple chemical sensitivity—every medical specialty has at least one (Table 1). There is much in common between these syndromes, epidemiologically, phenomenologically, and clinically, in terms of history, treatment, and doctor-patient relationships (6). Although the division of syndromes into the medically explained and unexplained is too simplistic for the complex etiology of modern medicine, it remains the case that no confirmed organic etiological markers have been found to distinguish the FSS. The lack of distinguishing pathophysiology, combined with the evidence of commonality, has led some researchers to propose that these syndromes may be manifestations of the same illness (6,7). In this article, we will selectively review the evidence for and against that proposal.
|
Are There More Similarities Than Differences in the Phenomenology of the Functional Somatic Syndromes?
A glance at Table 1 reveals a group of syndromes that would seem to have little in common, other than the absence of an accepted, clear-cut etiology. In particular, the symptoms after which most are named suggest little overlap, being segregated by physiological system. So it is perhaps surprising that anyone would think "irritable bowel syndrome" (IBS) an associate of "tension headache." But the neat taxonomy suggested by Table 1 belies the diversity of symptoms involved in the presentation of these syndromes: it is extremely common for those with irritable bowel symptoms to also report headache (8), and vice versa (9). The lists of symptoms reported by patients with these conditions are long, and overlap considerably. Furthermore, the etiological relationships suggested by such names as "tension headache" or "multiple chemical sensitivity" are either speculative, or, as in "premenstrual syndrome," descriptive. This is clearly seen when the names of these syndromes are compared across languages or cultures. The term for Irritable Bowel Syndrome is "Spasmodic Colitis" in French, for example, whereas Hyperventilation Syndrome is known as "Spasmophilia." The French terms suggest different pathophysiologies from their English counterparts. The names of our FSS may be suggestive, in short, but at present, none are etiological.
Without the organizing principles afforded by determinate etiology or pathophysiology, the FSS are characterized by their symptoms. In the spirit popularized by Diagnostic and Statistical Manual, 3rd Edition (DSM-III) (10), their diagnostic criteria tend to be given by checklists of these symptoms. One can therefore compare the phenomenology of the FSS by comparing their symptom checklists.
Do the Criteria Overlap?
Wessely et al. (6) considered this question in regard to 12 FSS for which criteria were available. They found considerable overlap in symptoms—bloating or abdominal distension in 8, headache in 6, abdominal pain in 6, fatigue in 6, and so on.
So, it is unsurprising that an examination of symptom prevalence by syndrome reveals considerable overlap. Although all patients with chronic fatigue syndrome (CFS) report fatigue, for example, 86% of patients with fibromyalgia (FM) do too; conversely, although all FM patients report arthralgia, so do 88% of CFS patients (11).
But what does this simple overlap tell us? Fatigue and pain are such ubiquitous features of illness that their involvement gives us few clues about disease processes: most diseases will have one or both as a symptom. Subarachnoid hemorrhage and meningitis may have almost 100% overlap in headaches without any suggestion that the boundary between them is blurred in any other important sense. Just sharing a symptom does not tell us much.
A more useful way of looking at the overlap may come from dividing the criteria into essential features and supporting (or "accidental") features. The essential features of subarachnoid hemorrhage and meningitis are blood in the cerebrospinal fluid and meningeal inflammation, respectively. A headache supports either diagnosis, and may be a fundamental part of the patient's experience, but is not part of the diagnostic criteria: asymptomatic meningitis, for example, would be meningitis nonetheless. The situation for the FSS is different because the lack of discrete pathology means both essential and supporting features will be symptoms. Still, it makes sense that fatigue should be the essential symptom of CFS, for example, and arthralgia should be a symptom that supports the diagnosis, but is not required. This structuring of criteria has been used in most FSS, which do not adopt simple checklists, but rather "Chinese Menu"-style criteria, where some symptoms are essential, and others are merely supportive. The 1994 Centers for Disease Control (CDC) criteria for CFS (12), for example, require at least 6 months of persistent fatigue (essential feature) plus 
4 (supporting) features from a list including sore throat, tender glands, headaches, and so on. FM, by contrast, is diagnosed solely by two essential features—musculoskeletal pain and the presence of tender points (13)—and all other reported symptoms, such as fatigue, may support the diagnosis, but are not required.
This is an attractive approach to classification, but it conceals a problem. The division into essential and accidental features comes originally from Aristotle (14), who argued that man, for example, was essentially rational, but only accidentally bipedal. Although this makes good sense for "man," it makes much less sense for any particular man, who is both bipedal and rational, to ask which is essential to him—his being bipedal is essential to him being "ambulatory," for example (15). Similarly, for any patient or group of patients, it is not clear why any symptom should be considered essential, unless it is to some prior conception, or some purpose. The meningeal inflammation is essential to meningitis because it provides an explanatory basis for the whole clinical picture of symptoms and therapeutics. But why should a patient's fatigue be essential, and not his/her pain? It might seem obvious that fatigue should be essential to chronic fatigue syndrome, but we must remember that "chronic fatigue syndrome" was constructed on the basis of symptom profiles: and for every symptom considered essential to that construct, there were equally many symptoms rejected (16).
Why should we not consider this construct to be arbitrary? Several reasons suggest themselves. First, the construct might reliably identify a separate group of patients from the symptom combinations of other FSS. Second, the group identified might differ from other FSS groups in other ways—epidemiologically, physiologically, or therapeutically. Third, the groups might differ in some important psychological respects. We shall consider each of these in turn.
If You Fulfill Criteria for One Syndrome, Do You for Others?
If FM and CFS were really (aspects of) the same underlying condition, then a high degree of comorbidity would be expected, but could not be explained by simple overlap of the diagnostic criteria. For meningitis and subarachnoid hemorrhage, focusing on the essential features of the disease rather than the headache identifies separate groups of patients, with almost no diagnostic overlap—no comorbidity of hemorrhage and meningitis: does the same hold for FSS?
Patients with one FSS almost universally report symptoms of others (11). Wessely et al. (6) drew attention to the literature reporting the symptomatic overlaps between, on the one hand, CFS and, on the other hand, fibromyalgia, tension headache, multiple chemical sensitivity, food allergy, premenstrual syndrome, and IBS. IBS was likewise associated with symptoms of hyperventilation syndrome, FM, CFS, tension headache, atypical facial pain, noncardiac chest pain, chronic pelvic pain, nonulcer dyspepsia, and premenstrual syndrome.
Wessely et al considered symptoms, however, not diagnostic criteria, which are more complex for a variety of reasons—the structuring into essential and supporting symptoms, the time course requirements, and the requirement for severity or functional impairment. Fortunately, many other studies have used diagnostic criteria, rather than symptoms. Aaron and Buchwald reviewed 53 studies where patients with one FSS were assessed by the formal diagnostic criteria for another (17). They found that 35% to 70% of patients with CFS met the criteria for FM, 58% to 92% met the criteria for IBS, and 53% to 67% showed multiple chemical sensitivity. Similarly, 75% of patients with FM met the criteria for temporomandibular disorder, 32% to 80% met the criteria for IBS, and 55% described multiple chemical sensitivity. Equally high rates were found for IBS, but for other, less studied disorders, such as temporomandibular disease and interstitial cystitis, the rates of concordance seemed to be lower. In a more recent large Swedish twin study, Kato et al. (18) looked at the comorbidities of chronic widespread pain as the cardinal symptom of FM. They reported considerable co-occurrences with CFS (odds ratio (OR) = 23.2), depressive symptoms (OR = 7.4), and IBS (OR = 5.3). The authors used co-twin analysis to demonstrate that these associations were extensively mediated by unmeasured genetic and family environment factors. But although these fully explained the psychiatric comorbidity, ORs remained >3 for CFS and IBS. There is still something about (meeting the criteria for) one FSS that makes another comorbid FSS more likely.
So, it seems that not only do the criteria for FSS often overlap, but so do the patients identified by those diagnoses. Even in cases where the diagnostic criteria do not refer to the essential features of another disorder, the criteria continue to identify the same patients: 70% of patients with FM meet the criteria for CFS (19), even though pain and tenderness do not appear in the essential criteria for CFS. As long as these syndromes are defined solely on the basis of symptom profiles, it can seem that the same patients, with the same symptoms, are being diagnosed one way or another on the basis of some arbitrary selection of these symptoms.
But even diagnostic criteria do not fully exhaust the factors that enter into making a diagnosis: the judgment of doctors and the presentation of patients will both have an impact. So, it is possible that when it comes to making an actual diagnosis that some factor in the clinic room determines that a patient has CFS or IBS. Yet, even where recent, large-scale studies have looked at the rates of comorbid diagnoses actually made, they still find increased rates of, for example, FM in IBS patients (OR =1.8) (20), and vice versa (risk ratio of 4.4 in women, 3.9 in men) (21). These results are striking because one would expect physicians to avoid making multiple diagnoses where possible. However, cohort studies of this kind are less good at detecting true comorbidity because they do not rely on primary clinical data. The increased rates may therefore represent a degree of pathoplasticity, or changes in diagnosis, rather than true comorbidity. Although there is some evidence of pathoplasticity (22), population-based studies (16,23,24) find that the fatigue syndrome, for example, is stable.
We should acknowledge the interest of the specialist physician here. The same patient could be diagnosed with temporomandibular disorder by the oral surgeon and then with FM by the rheumatologist; thus, the apparent diversity of syndromes may be no more than an artifact of medical specialization (6,19).
In summary, at every level of clinical-phenomenological assessment—symptoms, criteria, and actual diagnoses—there are greatly increased rates of comorbidity, of overlap. This lends support, as far as it goes, for those who would argue that the FSS are all one, or at least closely related. But the phenomenological is only one consideration—the FSS may differ in many other respects.
Do the Syndromes Differ in Other Ways?
The perceived commonalities of epidemiology, psychosocial risks, management, and outcome, when combined with the absence of pathognomonic tests and overlapping symptoms, have historically led some researchers to suggest that the similarities outweigh the differences between these syndromes. Freud's is perhaps the most famous attempt to group medically unexplained symptoms under a single model (25), though it was not the first, or the last. More recently, it has been argued that the FSS are still substantially similar in these respects (6), although not everyone is persuaded (26). These other aspects are explored in this special issue. Suffice it to say, the commonalities remain impressive, and the increasing number of differences is intriguing. The interpretation of these, however, is more complex still.
Let us consider one illustrative recent finding that different infective organisms differentially precipitate CFS and IBS (27). This is clear evidence that CFS and IBS are different. But different in what way? In the way that a staphylococcal dermatitis differs from a streptococcal dermatitis? Or in the way that a streptococcal dermatitis differs from a streptococcal meningitis? In both of these senses, there are important differences and important commonalities; whether we want to consider a streptococcal dermatitis different from a meningitis depends on our purpose: the way we classify is ultimately instrumental. Classifying by infective organism is no more "real" than classifying by organ system—they each have their utility. What purpose, then, could it serve to consider CFS and IBS the same, if their etiological risks are essentially different and their symptoms perhaps only accidentally similar? One answer could be that it may serve to describe a commonality of disease process, of the psychosocial role in the generation, maintenance, and treatment of symptoms.
Does This Mean They Are All Psychosomatic?
No. Although a psychosomatic view of FSS has been popular in the past, it is by no means implied by the "one syndrome" hypothesis (26)—even if, as seems probable, the psychosocial is relevant to the etiology, pathophysiology, and management of FSS. The relationship of the psychosocial and psychiatric with FSS is explored elsewhere in this issue. But the same sorts of questions of overlap that we have discussed here have been explored with respect to the FSS, anxiety, and depression. There is no doubt that there is a relationship between them, although it is complex (28). For CFS, there is a linear relationship between the number of CDC symptoms and psychiatric morbidity (16), and this cannot be explained simply as a psychological reaction to physical illness and/or disability (28). But the high rates of psychiatric morbidity are far from sufficient to explain the prevalence of FSS.
Another clear relevance of the psychosocial view is in treatment, where cognitive behavioral therapies have shown success in a number of FSS (29). These therapies offer cognitive-behavioral models for symptom persistence and, in some cases, symptom generation. More generally, it is a platitude that all symptoms are cognitively mediated. But this is not the same as a "psychosomatic" or "imaginary" model: sleep in CFS really is disturbed, and may have been provoked by any number of organic illnesses, for all that a cognitive-behavioral cycle can be argued to sustain the disturbance. The patient's beliefs about his/her illness play a key role in the cognitive model and in the presentation of that illness (30). This idea, of the centrality of the psychosocial role, may serve as a kind of grouping principle, as an important way in which the FSS are importantly thought to be the same; but equally, the specific psychosocial roles in each FSS reveal another way in which they differ.
The Patient's Perspective
In this discussion of the different perspectives from which the FSS may be considered, we finally come round to the patient's perspective. Giving a diagnostic label has potentially huge significance for the patient (31) and which particular diagnostic label may make a considerable difference (32). This is not to reanimate the moribund antipsychiatry view that the label is all. Disposing of the schizophrenia label does not abolish psychosis, or the problems of patients with psychotic symptoms. But we do accept that labels shape and reflect how patients respond to illness. CFS and FM, for example, are the syndromes where there is arguably the greatest overlap, including in their response to graded exercise (33,34); yet, a glance at online discussion groups reveals dramatically different views on its application between the two disorders.
If a diagnostic system divided along the lines of medical specialties seems arbitrary, one that accords with patients' views is the height of pragmatism (35). Where diagnoses are contentious, and the evidence base for one system or another is limited, a classification that minimizes conflict may serve far more effectively as a platform for recovery (31).
The Same But Different
For all the commonality, the differences between the FSS cannot be ignored. Although there are substantial overlaps in symptoms and patients, these are far from universal. A latent variable analysis of patients with somatic symptoms (36), suggested a best fit of a five-factor model—CFS-like, IBS-like, FM-like, depression, and anxiety—but also a large common factor: yes, they had much in common, and no, they are not the same. For some classificatory purposes, it may be best to consider the FSS as the same, and for other purposes as different. Although this may seem pusillanimous, we should remember that all our scientific classifications are instrumental: light is both a wave, and in other contexts a particle, and, with our current understanding, there is simply no better, no more truthful way to describe it (37). In the FSS, a diagnosis that respects the patient's view of his/her illness stands to be both instrumentally and pragmatically apt.
NOTES
Received for publication March 7, 2007; revision received May 31, 2007.
Richard A. A. Kanaan, MRCPsych, was supported by a Biomedical Ethics Fellowship from the Welcome Trust (079743).
This article is being co-published by Psychosomatic Medicine and the American Psychiatric Association.
DOI:10.1097/PSY.0b013e31815b001a
REFERENCES
This article has been cited by other articles:
 |
|
 |
|
  S. Skovbjerg, S. Brorson, A. Rasmussen, J. D. Johansen, and J. Elberling Impact of self-reported multiple chemical sensitivity on everyday life: A qualitative study Scand J Public Health, August 1, 2009; 37(6): 621 - 626. [Abstract] [PDF]
|
|
|
|
 |
|
 J. E. Dimsdale, V. Patel, Y. Xin, and A. Kleinman Somatic Presentations A Challenge for DSM-V Psychosom Med, November 1, 2007; 69(9): 829 - 829. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
