Symptoms without pathology: should we try a little tenderness?

P. Croft

Primary Care Sciences Research Centre, Keele University, Keele, Staffordshire ST5 5BG, UK

One approach to fibromyalgia is to regard it as being at one end of a spectrum of musculoskeletal pain and somatic symptoms. A steady flow of studies on fibromyalgia in the past two decades suggests that researchers themselves lie on a spectrum, ranging from those who accept the existence of fibromyalgia as a discrete clinical condition and investigate its causes, correlates and treatments, to those who dismantle it and attempt to investigate its component parts. There is general support for the idea that criteria such as those published by the American College of Rheumatology (ACR) have ‘provided a common language for researchers' [1], but less agreement on what exactly we are dealing with in clinical practice. What exactly is fibromyalgia?

Epidemiologists have steered towards chronic widespread pain as being the key characteristic, sometimes adding high tender point counts to define the subgroup with ‘fibromyalgia’. However, there is general acceptance that chronic widespread pain itself is an arbitrary category that includes people with more severe, extensive and persistent pain than non-widespread or regional pain sufferers. It is not clear what clinicians opt for in practice. Do rheumatologists tend to work with some concept of widespread musculoskeletal pain with no obvious immediate pathological cause? Or are most clinicians, following the lead of those who write on the topic of fibromyalgia, adding in some tender points as well?

This is important. If fibromyalgia is chronic pain writ large, then there may be nothing apart from the degree of pain to distinguish it from conditions such as chronic low back pain. If there is something about fibromyalgia which is qualitatively different from chronic regional pain, it may give clues to the whole nature of pain chronicity and its prevention. Tender points might be one marker of such a qualitative difference. The difficulty has been that they do not have a clear conceptual basis. What do tender points actually stand for?

In a succinct summary of experimental studies into fibromyalgia, Crofford and Clauw took it as given that tender points represent abnormal processing of pain, and reviewed evidence that tenderness to pressure represents a phenomenon different from the actual expression and reporting of pain [1]. They pointed to convincing evidence that groups of patients meeting the ACR diagnostic criteria for fibromyalgia show differences from comparison groups, both in their responses to experimental pain and in markers of those physiological processes that may influence pain experience (such as the neuroendocrine stress response system). What remains to be clarified is how specific to fibromyalgia are such abnormalities, and whether they are epiphenomena or causes of the pain experience itself.

Epidemiologically, there have been surprisingly few attempts to investigate tender points as a population phenomenon in their own right. Some investigators have included examination of tender points in people identified as having chronic widespread pain in population surveys in order to provide estimates of prevalence of the fibromyalgia syndrome [e.g. 2, 3]. Other population and clinic studies in the 1990s found that people with regional pain and no pain could also have high tender point counts, and that psychological distress and sleep problems became more prominent with a higher tender point count independently of the presence or extent of pain [4, 5]. This suggested that tender points do represent something separate from the experience and reporting of chronic pain. But what, exactly?

A UK study reported on 289 people identified from a population-based sample of people with psychological distress, who had a tender point examination [6]. Those with tender point counts of 5 or higher were more likely than those with lower counts to report somatic symptoms other than pain, fatigue and high use of health-care; an important point was that these findings were not explained by chronic pain. A study from Sweden suggested that tender points, although strongly correlated with pain reporting, were independently associated with other symptoms and with some items of disability [7]. Such investigations suggested that the presence of multiple tender points might be related more generally to the presence of somatic symptoms—those syndromes and conditions variously referred to as ‘unexplained clinical conditions' or ‘functional syndromes’, and which include such problems as chronic fatigue and irritable bowel syndrome—and not simply to the presence of associated widespread pain. A review of studies of the overlap between these syndromes added force to this conclusion by identifying tender points on physical examination as the most consistent and objective finding across the different symptom complexes [8].

Schochat and Raspe [9], in a new study reported in this issue of Rheumatology, take the empirical study of tender points a stage further. In their population-based survey, they have confirmed that high tender point counts occur in the absence of chronic pain. However, they have focused attention on other common somatic symptoms, and neatly stratified their pain groups by high and low levels of these other symptoms. Although, as expected, tenderness goes up with pain, the tender point count also goes up with other symptoms independently of pain. Tenderness in this carefully constructed population investigation is a general marker for the presence of multiple symptoms other than pain.

There seem to be two broad possible explanations for this finding. First, it gives some support to the theory that there is an underlying pathological link between unexplained chronic functional syndromes which overlap and co-occur in both general population and clinic settings [10]. Although the actual mechanism for tenderness in the absence of pain is unclear, ‘latent central pain processing’ might be a manifestation of broader abnormalities—in the stress response for example—which have effects on multiple tissues and organ systems. Secondly, this might be about somatization—the expression of social or psychological distress as physical symptoms. In this model, there is a spectrum of unexplained somatic symptoms, which, among people without chronic widespread pain, for example, predict the subsequent onset of chronic widespread pain [11]. Tenderness becomes another facet of this, even when pain is not expressed. However, a particularly intriguing aspect of Schochat and Raspe's study is what happened when they incorporated a number of measures, other than somatic symptom count and the presence of pain, in a multivariate model of potential associations with tender points. These other measures included the extent of pain, depression, other measures of emotional difficulties, unhelpful cognitions, social isolation and physical mobility. Four independent predictors of high tender point counts emerged from this model: age, presence of pain, restricted physical mobility—and a high somatic symptom count. Psychological factors were not independently associated with a high tender point count in this population, but were linked separately to chronic widespread pain. This finding is at odds with some of the earlier studies [4, 6], and argues against the idea that tenderness simply represents somatization of distress. Schochat and Raspe's study is important because it was not limited to a particular subgroup and it included a high somatic symptom score as a distinct variable. Furthermore, it is in accord with an American study of tenderness in acute infectious mononucleosis, which found no link between tender point count and psychological distress or psychiatric illness [12].

Schochat and Raspe's study gives empirical support to the existence of a cluster of somatic symptoms, to which tenderness appears to have claims on membership in its own right and not only as a surrogate for chronic widespread pain. But, as the authors themselves point out, this also means undermining the idea—which is such an important feature of the clinical description of fibromyalgia—of a unique association between high tender point counts and chronic widespread pain. The message seems to be that rheumatologists do not have an exclusive claim on high tender point counts.

It looks as if tender points might be worth pursuing as part of the agenda of research into the phenotypes and mechanisms of symptoms without obvious pathology, of which chronic widespread pain is but one example. The final question is whether tender point counts are useful in practice. White and colleagues have argued for this, and provided evidence that individual tender points appear to be proxies for high counts, which might make tenderness assessment a more practical routine for clinical practice [2]. Now Schochat and Raspe's work suggests that there may be merit in measuring tender point counts in their own right as a proxy assessment of ‘multiple somatic symptom syndrome’. But we are taken back to the original problem: what exactly would tender points be assessing? Even if clinicians do not know what precisely to do for patients' unexplained symptoms, they will still try to ameliorate these symptoms or help patients with approaches that reduce the impact of such problems on everyday lives, as a guiding principle of their clinical endeavour. If tender points guided the choice or targeting of interventions in a way which enhanced the value of this endeavour, or if treating tenderness was a sensible route to reducing the severity or impact of symptoms, or even if the demonstration of tenderness provided a useful characterization of the problem for the clinician to provide to the patient, the clinical usefulness of counting up tender points might be more obvious. There is as yet no empirical evidence that they are useful or valuable in the clinical setting, and for the moment they must still be regarded as an interesting tool for clinical research, to which the German study has added more weight and more interesting questions to be addressed.

Notes

E-mail: p.r.croft{at}cphc.keele.ac.uk Back

References

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