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Somatization: A Critical Review of Conceptual and Methodological Issues

Received May 9, 2001; revised October 12, 2001; accepted October 25, 2001. From the Faculty of Medicine, Catholic University Leuven, and the Department of Liaison Psychiatry, University Hospital of Gasthuisberg, Leuven, Belgium. Address correspondence and reprint requests to Dr. De Gucht, Department of Clinical and Health Psychology, Leiden University, Wassenaarseweg 52, P.O. Box 9555, 2300RB Leiden, the Netherlands. E-mail: veronique.degucht{at}belgacom.net

ABSTRACT

TOP ABSTRACT INTRODUCTION THE CONCEPT OF SOMATIZATION:... PRESENTING AND FUNCTIONAL... IMPORTANT MEASUREMENT ISSUES... GENERAL DISCUSSION AND... REFERENCES

 
Despite its apparent clinical importance and the extensive research that has been conducted in the past decades, somatization remains a complex concept. Two distinct ways of looking at somatization can be distinguished: somatization as a phenomenon that is secondary to psychological distress (presenting somatization) and somatization as a primary phenomenon characterized by medically unexplained symptoms (functional somatization). The literature was analyzed in terms of this distinction and a selective review was conducted, focusing on a critical analysis of conceptual and methodological issues related to presenting and functional somatization. A number of measurement issues related to somatization in general were also highlighted. On the basis of the available data, the strengths and weaknesses of different concepts are pointed out. Conclusions are formulated regarding which concepts or approaches might be useful both clinically and from a research perspective. Finally, a number of suggestions for future research are offered.

Key Words: Somatization • Assessment • Medically Unexplained Issues

INTRODUCTION

TOP ABSTRACT INTRODUCTION THE CONCEPT OF SOMATIZATION:... PRESENTING AND FUNCTIONAL... IMPORTANT MEASUREMENT ISSUES... GENERAL DISCUSSION AND... REFERENCES

 
Somatization has been defined in a number of different ways. Despite their differences, these definitions have one element in common, namely the presence of somatic symptoms that cannot be (adequately) explained by organic findings. Epidemiologic studies have demonstrated a high prevalence of such symptoms in the general population¹ and in all medical settings.^2,3 Chronic or recurrent forms of somatization lead to an increased utilization of health care resources, increased disability, and an elevated number of days off work.^4–6 On the basis of this, one can consider somatization to be an important clinical phenomenon and socioeconomic problem because it leads to considerable costs, both direct and indirect. The fact that new concepts related to somatization have been developed recently^6,7 clearly points to a renewed interest in and a conceptual revival in somatization research.

Despite the apparent clinical importance of somatization and the extensive review literature on the subject,^8–11 the theoretical concept remains a complex and difficult one. This is mainly because, from the start, somatization has been defined in two distinct ways, reflecting different approaches to the same fundamental problem. In addition, several new conceptualizations and measurement procedures for somatization have been developed in recent years, complicating even more the field of somatization. To the best of our knowledge, no comprehensive review has addressed both the conceptual and methodological issues related to somatization. The present review was conducted to fill this gap.

Our objectives are: 1) to describe briefly the historical evolution of the somatization concept and the different approaches that have resulted from this evolution; 2) to analyze the empirical literature on presenting and functional somatization in terms of conceptual developments and methodological issues; 3) to describe a number of important problems related to the measurement of somatization in general; and 4) to draw conclusions about which concept(s) might be considered useful both clinically and from a research perspective and to evaluate possible avenues for future research.

THE CONCEPT OF SOMATIZATION: HISTORY AND DEFINITION

TOP ABSTRACT INTRODUCTION THE CONCEPT OF SOMATIZATION:... PRESENTING AND FUNCTIONAL... IMPORTANT MEASUREMENT ISSUES... GENERAL DISCUSSION AND... REFERENCES

 
Hysteria
Briquet¹² was the first to study a syndrome characterized by multiple somatic symptoms, which he called hysteria. In contrast to Briquet, Freud¹³ distinguished between two different phenomena characterized by the presence of somatic symptoms, namely conversion hysteria and neurasthenia. Both concepts were theoretically distinct, with conversion hysteria (a psychoneurosis) being defined as psychic in origin (i.e., symptoms are the symbolic expression of infantile sexual conflicts), and neurasthenia (an actual neurosis) being defined as somatic in origin (i.e., symptoms are a direct consequence of unresolved sexual tension in the present). Briquet's hysteria concept was further developed by Purtell et al.¹⁴ and operationalized by Perley and Guze.¹⁵ Hysteria, as defined by these authors, was characterized not only by the presence of multiple somatic complaints, but also by anxiety and depressive symptoms. This concept of hysteria was the precursor of somatization disorder (SD) as defined in DSM-III.¹⁶ The major difference between the newly defined SD and the former concept of hysteria was that anxiety and depressive symptoms were no longer part of the diagnostic criteria. It is interesting to note that it is exactly the relation between somatization, anxiety, and depression that is at the heart of the two distinct ways in which somatization has been conceptualized, namely as a somatic manifestation of psychological distress on the one hand, and as somatic distress or the experience of medically unexplained symptoms on the other hand.

Somatization as a Somatic Manifestation of Psychological Distress
The concept of somatization was first used by Stekel,¹⁷ who defined it as a bodily disorder arising as the expression of a deep-seated neurosis. Some early definitions of somatization clearly remind us of these psychodynamic roots. The definition put forward by Lipowski in 1968 was a classic example of this; he described somatization as "the tendency to experience, conceptualize and/or communicate psychological states or contents as bodily sensations, functional changes or somatic metaphors."¹⁸ Nineteen years later, he changed this definition into "a tendency to experience and communicate psychological distress in the form of somatic symptoms and to seek medical help for them."¹⁹ Although less influenced by psychoanalysis, this definition still suggested the existence of a causal relation between the experience of psychological distress and the presentation of somatic symptoms. The operational criteria for somatization developed by Bridges and Goldberg²⁰ are in line with this, as they clearly conceptualized somatization as a somatic expression of an Axis I psychiatric disorder. In addition to Lipowski¹⁹ and Bridges and Goldberg,²⁰ a number of other authors^21–24 have used definitions that all share one central feature, namely that somatization is considered the somatic manifestation of psychological distress or an Axis I psychiatric disorder.

Somatization as Somatic Distress
A whole range of definitions of somatization are characterized by the assumption that the presentation of somatic symptoms is the hallmark of somatization, to the exclusion of assumptions about causality. Lipowski's key article in 1988²⁵ could have paved the way for this development because it is in this paper that he first adopted a more descriptive definition of somatization. In particular, he defined somatization as "the tendency to experience and communicate somatic distress and symptoms unaccounted for by pathological findings, to attribute them to physical illness, and to seek medical help for them."²⁵ In contrast to his earlier definitions, he proceeded carefully, stating that "it is usually assumed that this tendency (to somatize) becomes manifest in response to psychosocial stress."²⁵

Within this conceptualization of somatization, three progressively more restrictive orientations can be distinguished. The first of these, equating somatization with simple symptom counting, can be defined as somatization in the broadest sense.²⁶ Because of the lack of clinical specificity of this concept, Mayou²⁷ proposed to use a more general term, such as nonorganic physical symptoms or medically unexplained symptoms, for this phenomenon. The second orientation, introducing a criterion of severity (e.g., the chronic or recurrent character of the symptoms, the number of symptom groups involved, the degree of associated disability, and medical consumption), can be illustrated by the definition of SD in DSM-III,¹⁶ DSM-III-R,²⁸ DSM-IV,²⁹ the tenth edition of the International Classification of Diseases (ICD-10) of the World Health Organization (WHO),³⁰ the Somatic Symptom Index (SSI),³¹ and the multisomatoform disorder.⁶ Finally, the third orientation reintroduces a theoretical dimension because it considers specific cognitive and/or behavioral characteristics as a necessary part of somatization. The definitions of Lipowski,²⁵ Barsky,³² and Rief and Hiller⁷ are representative of this orientation.

Presenting and Functional Somatization
Within primary care, Kirmayer and Robbins³³ studied the aforementioned somatization concepts as two separate clinical phenomena, termed "presenting somatization" and "functional somatization." Whereas presenting somatization was defined as "the predominantly or exclusively somatic presentation of psychiatric disorder, most commonly depression and anxiety,"³³ functional somatization referred to "high levels of medically unexplained symptom reporting in multiple physiological systems."³³ Kirmayer and Robbins,³³ and also Garcia-Campayo et al.,³⁴ have demonstrated that presenting and functional somatization tend to identify two distinct groups of patients, with some degree of overlap between them. The distinction that was made by Kirmayer and Robbins has also been described by other authors, using slightly different names.^35–38

PRESENTING AND FUNCTIONAL SOMATIZATION: CONCEPTUAL AND METHODOLOGICAL ISSUES

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The empirical literature related to presenting and functional somatization (1980–2000) was analyzed in terms of conceptual developments and methodological issues. The focus was not only on the leading concepts in the domain of somatization, but also on studies that have laid the foundation for the development of new, operationally defined, concepts.

Presenting Somatization
Whereas this line of research started with Bridges and Goldberg,²⁰ Kirmayer and Robbins³³ and Craig et al.³⁹ have succeeded in introducing important refinements, both from a conceptual and a methodological perspective.

Conceptual Developments
In the primary care studies of Bridges and Goldberg²⁰ and Bridges et al.,⁴⁰ patients were identified as somatizers if they presented only with somatic symptoms to their primary care physician, if they attributed these symptoms to a physical problem, and if they were subsequently diagnosed by a research psychiatrist with a psychiatric disorder. From a conceptual point of view, it is important to emphasize that a causal relation was assumed between the somatic symptoms the patients presented with and the psychiatric disorder subsequently diagnosed. In addition, treatment of the psychiatric disorder was expected to reduce or eliminate the somatic symptoms.

When defining presenting somatization, Kirmayer and Robbins³³ directly referred to Bridges and Goldberg,²⁰ but at the same time they introduced two important modifications to their operational criteria. First of all, they considered the connection between the somatic symptoms reported by the patient and the psychiatric disorder subsequently diagnosed as a research question, not an a priori fact. In other words, the existence of a causal relation was not considered self-evident. Second, they emphasized the difficulty of putting into practice the assumption that in treating the underlying psychiatric disorder, the somatic symptoms would disappear. Leaving out these two characteristics, the criteria of Kirmayer and Robbins³³ for presenting somatization required that patients: 1) reach the diagnostic threshold for major depression or an anxiety disorder, 2) present to their physician only with nonorganic physical symptoms, 3) make only somatic attributions, and 4) reject psychosocial attributions for their symptoms. These criteria were intended to cover three increasingly persistent forms of presenting somatization, with "true somatizers" satisfying all four criteria, "facultative somatizers" satisfying the first three criteria, and "initial somatizers" satisfying only the first and second criteria.^33,41 Later studies on presenting somatization have not led to any further conceptual changes.⁴²

Methodological Issues
Two methodological inadequacies are clearly present in the studies by Bridges and Goldberg²⁰ and Bridges et al.,⁴⁰ namely: 1) no objective medical information was consulted to exclude organic causes for presenting symptoms, and 2) the assumption of a causal relation between somatic symptoms and psychiatric disorders was based exclusively on the subjective judgment of the research psychiatrist, without putting this assumption to the test.

On the basis of the South London Somatisation Study, a 2-year follow-up study in primary care, Craig et al.³⁹ succeeded in solving these methodological flaws. First of all, the judgment of whether a symptom was medically explained or not was based on objective medical information. Second, to avoid the pitfall of subjective judgment, two independent raters measured the presence of psychiatric disorder and the nature of the somatic symptoms (medically unexplained versus medically explained). In addition, Craig et al.³⁹ tried to test the assumption that the somatic symptoms the patient presented with were indeed a manifestation of the psychiatric disorder that was diagnosed. They demonstrated, both in the index period and at follow-up, that there was a temporal association between changes in the severity of the psychiatric disorder and the severity of somatic symptoms. No relation was found between specific symptoms and particular psychiatric disorders.

Functional Somatization
Conceptual Developments
The major conceptualizations of functional somatization are SD as defined in DSM-III,¹⁶ DSM-III-R,²⁸ DSM-IV,²⁹ and ICD-10,³⁰ although a number of subsyndromal variations on SD exist, such as the SSI³¹ and the more recently developed multisomatoform disorder⁶ and polysymptomatic somatoform disorder.⁷

Table 1 presents a description of the defining characteristics of each of these concepts. To highlight the differences and similarities between them, each of the concepts is described according to the same dimensions, namely: 1) the number of medically unexplained somatic symptoms required (symptom cutoff); 2) the duration of the symptoms, representing a continuum from current to lifetime; 3) the presence or absence of criteria of severity, such as interference with life and medical consumption; 4) the number of symptom groups that are required; and 5) the presence or absence of specific psychological characteristics.

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TABLE 1. Characteristics of the different concepts related to functional somatization

Methodological Issues (1): Validity of Symptom Cutoffs
The symptom cutoffs used to define SD in the subsequent versions of DSM (Table 1) have their origin in the operational criteria for hysteria developed by Perley and Guze.¹⁵ These criteria were subsequently integrated by Feighner et al.,⁴³ and their validity was established.⁴⁴ A modified version of the Feighner criteria provided the foundation for the description of SD in DSM-III.¹⁶ For this purpose, the original 59-item symptom list used to diagnose hysteria was shortened to 37 on the basis of a statistical analysis by Guze on his original sample.⁴⁵ The total number of symptoms required for a positive diagnosis was reduced from 25 to 14 symptoms in women and 12 in men. Attempts at validating these new criteria resulted in concordances between the original Feighner criteria and DSM-III criteria for SD ranging between 71%⁴⁶ and 90%.⁴⁷ In DSM-III-R,²⁸ the criteria for SD were further modified. The symptom list was reduced to 35, and the number of symptoms required for a diagnosis of SD was made the same for men and women. In DSM-IV, the criteria for SD were further simplified on the basis of Cloninger's reanalysis of data on 500 psychiatric outpatients.⁴⁶ This reanalysis revealed that SD could be diagnosed reliably by requiring the presence of at least 8 symptoms coming from 4 clearly defined symptom groups. The results of the DSM-IV field trial,⁴⁸ the purpose of which was to validate the newly defined SD, demonstrated a high level of concordance among the diagnostic criteria for SD according to DSM-IV, DSM-III-R, DSM-III, and the original Feighner criteria.

In introducing the diagnostic entity of SD in the research criteria of the ICD-10,³⁰ WHO has followed the American lead. It remains unclear, however, on what basis the symptom cutoff for a diagnosis of SD has been selected. The DSM-IV field trial⁴⁸ revealed a poor agreement between ICD-10 and the different DSM criteria as well as the Feighner criteria.⁴³

In an attempt to offer a diagnostic label for those patients with a high number of medically unexplained symptoms who did not reach the diagnostic threshold for SD according to DSM-III, Escobar et al. developed the SSI.³¹ The empirical basis of the proposed cutoff was weak, however. The cutoff of four symptoms for men and six symptoms for women was chosen because it discriminated significantly between Hispanic and non-Hispanic white male subjects with schizophrenia.⁴⁹ This can hardly be considered a theoretically valid basis. Escobar et al. subsequently tested the value of the SSI in the general population^31,50 and in primary care.² The fact that the SSI was found to be a good predictor of important outcome variables, such as disability and the use of health services, may justify its continued use.

The cutoff of three symptoms to define multisomatoform disorder⁶ was selected primarily because of its predictive validity with respect to disability. Further reasons mentioned by the authors (K. Kroenke, personal communication, June 9, 2000) are that three symptoms make a single explanatory medical disorder less likely than one or two symptoms, and that multisomatoform disorder attains a reasonable prevalence of 8% when using a cutoff of three symptoms.

Accordingly, a cutoff of seven symptoms has been selected to define the polysymptomatic somatoform disorder⁷ because of its discriminative power with respect to disability.

Methodological Issues (2): Assessment
Escobar^31,49,50 studied the phenomenon of somatization primarily within the framework of the Epidemiological Catchment Area (ECA) study. The major problem with the ECA study, as with most epidemiologic studies on SD, is that the structured psychiatric interviews used to assess SD and the SSI were conducted by lay people. These lay interviewers could rely only on the subjective report of the study subjects and may have had difficulty distinguishing between symptoms that were due to organic causes and those that were not. A study comparing diagnoses based on lay interviews with diagnoses made by psychiatrists, both using the same structured diagnostic interview, found only moderate concordance between the approaches.⁵¹ In one of the ECA studies,³¹ a psychiatrist additionally checked each of the medically explained symptoms to decide whether the medical explanation given by the patient was a plausible one. He did not have access to the medical records of the study subjects, however, and was thus unable to check the symptoms reported by the subject against objective medical information.

Multisomatoform disorder⁶ is diagnosed on the basis of the Primary Care Evaluation of Mental Disorders (PRIME-MD).⁵² The PRIME-MD consists of two components: a patient questionnaire and a clinician evaluation guide, which is a structured interview that the primary care physician uses to follow up on positive responses on the patient questionnaire. The somatoform module of the PRIME-MD requires patients to fill out a 15-item symptom list to indicate those symptoms that have bothered them a lot for the past month. Three or more positive items direct the physician to the somatoform part of the clinician evaluation guide. The objective of this is to decide whether, based on the information contained in the patient's medical record, the symptoms that the patient is experiencing have a medical explanation that can adequately account for their severity.

Unlike the SSI and multisomatoform disorder, polysymptomatic somatoform disorder is diagnosed on the basis of a self-report scale, the Screening for Somatoform Disorders (SOMS).⁵³ The use of a self-report scale does not allow one to validly exclude organic origin. The fact that patients are requested to mark only those symptoms for which a sufficient medical explanation is lacking inevitably leads to an underestimation of somatization symptoms because patients cannot be expected to be reliable judges with respect to the nature of their symptoms. The authors stated that there was a high concordance between the diagnostic results of the SOMS and those of a structured psychiatric interview.⁵⁴ These data were obtained with a previous version of the SOMS, however.⁵⁵ In this version, the patients indicated the symptoms they had experienced during the past month, but the physician decided on the organicity of the symptoms by using the information contained in the patient's medical record and (previous) medical examination(s). The values reported by the authors (W. Rief, personal communication, May 2, 2000) with respect to the concordance between diagnoses on the basis of the more recent self-report SOMS and interview-based diagnoses are moderate (0.68 for DSM-IV SD and 0.57 for ICD-10 SD).

IMPORTANT MEASUREMENT ISSUES RELATED TO SOMATIZATION IN GENERAL

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Discussing each of the existing measurement and boundary issues is beyond the scope of this paper. Therefore, this brief overview will be limited to those measurement issues that are directly relevant to the concepts and methodologies that have been discussed so far.

Lifetime Assessment of Somatization
The WHO collaborative study of psychological problems in general health care⁵⁶ tackled a major methodological issue with respect to SD as defined in DSM-III,¹⁶ DSM-III-R,²⁸ and DSM-IV,²⁹ namely whether SD, defined as a chronic lifetime disorder, can be reliably measured. The results of the prospective part of the study clearly indicated that this was not the case because only 25% of the patients meeting criteria for SD at baseline also met these criteria 1 year later. Conversely, only 27% of patients meeting criteria for SD at follow-up also met these criteria 1 year earlier. In addition, 61% of lifetime symptoms reported at baseline were not reported at follow-up.⁵⁷ Given that both the baseline and follow-up assessments asked about lifetime symptoms, this marked discrepancy can only be attributed to inconsistent recall.

Distinguishing Medically Explained From Medically Unexplained Somatic Symptoms
The overall diagnosis of somatization is essentially based on the exclusion of organic causes for the somatic symptoms reported by the patient. In most cases, this is not problematic as long as the results of hospital referrals, diagnostic tests, and other relevant data from the patient's medical record are available to the researcher. It should be emphasized, however, that even if this is the case, there remain a number of instances in which it is difficult to decide whether a symptom is medically explained or not.

The existence of this kind of "borderline" symptom can be illustrated by several common complaints, such as low back pain in relation to the structural anomaly of disc herniation. Although low back pain is a somatic symptom in which morphologic anomalies can be measured, the criteria for anomalies on radiology or magnetic resonance imaging (MRI), suggestive of organicity, are not straightforward. First of all, disc herniation has been observed in many subjects who were asymptomatic.⁵⁸ Second, researchers demonstrated that the prognosis of pain reduction after surgery was related not to disc herniation per se, but to the degree of nerve compromise on MRI.⁵⁹ As a consequence, the exact status of low back pain is sometimes difficult to assess without detailed radiologic information, which is generally not available. In accordance with this, Creed et al.⁶⁰ demonstrated that in a sample of patients who were newly admitted to a neurology ward, one-third of the patients could not be confidently classified as suffering from either organic neurologic disease or somatization.

Closely related to the issue of borderline symptoms are those cases in which medically unexplained symptoms seem to be grafted onto an existing organic disease,⁶¹ as well as those cases in which residual symptoms remain after the organic disorder has been adequately treated.⁶² To some extent, the existence of this kind of problem related to somatization points out the limitations of a dualistic conceptualization of medical illness (medically explained symptoms) versus psychiatric disorder (medically unexplained symptoms).

Somatization: One Dimension or Several?
The factor-analytic studies that have been retrieved show evidence for the existence of both a large general somatization factor and several distinct clusters of symptoms (and patients).

In a general population sample, Liu et al.⁶³ demonstrated the occurrence of a strong, single, general somatization factor. Accordingly, on the basis of a reanalysis of the data, Deary⁶⁴ found that the syndrome-level latent traits of fibromyalgia, chronic fatigue, irritable bowel, somatic depression, and somatic anxiety, described by Robbins et al.⁶⁵ in primary care, accounted for little of the individual symptom variance. A large general somatization factor, however, accounted for 69% of the total variance. In contrast to these findings, Swartz et al.⁶⁶ and Gara et al.⁶⁷ demonstrated the existence of several clusters of patients who were characterized by distinct patterns of medically unexplained somatic symptoms. The validity of these clusters was supported by the fact that they tended to relate differently to psychiatric morbidity and disability.⁶⁷ In addition to the general somatization factor already mentioned, Liu et al.⁶³ found two more specific factors, different for males and females.

GENERAL DISCUSSION AND SUGGESTIONS FOR FUTURE RESEARCH

TOP ABSTRACT INTRODUCTION THE CONCEPT OF SOMATIZATION:... PRESENTING AND FUNCTIONAL... IMPORTANT MEASUREMENT ISSUES... GENERAL DISCUSSION AND... REFERENCES

 
Despite the huge number of publications devoted to the subject, somatization has remained a complex concept. In this paper, we argue that this may be partly due to the complex relation between psychological distress and somatic distress. Two different approaches to somatization have resulted from this relation: one that treats somatization as a phenomenon that is secondary to psychological distress (presenting somatization) and one that defines somatization as a primary phenomenon characterized by the presence of medically unexplained symptoms (functional somatization).

Both approaches have their pros and cons, both from a conceptual and a methodological perspective. A clear advantage of presenting somatization is that it draws attention to hidden psychiatric morbidity, especially anxiety and depressive disorders. A clear disadvantage of the concept is that it does not take into account patients who present with medically unexplained somatic symptoms without an underlying anxious or depressive disorder. This in turn is the major plus of functional somatization because it explicitly focuses on this phenomenon and establishes its relation to disability. From a methodological point of view, presenting somatization has the disadvantage of presuming a causal relation between anxiety or depression and medically unexplained somatic symptoms. Functional somatization, on the other hand, suffers from a multitude of concepts and associated symptom cutoffs and therefore is in need of clarification.

With respect to presenting somatization, the definition used by Craig et al. covers the concept well, namely "subjects with a psychiatric disorder who present to their general practitioner with physical complaints but in whom a functional diagnosis is recorded."³⁹ The facts that a substantial proportion of psychiatric morbidity in primary care remains undiagnosed⁶⁸ and that as many as 80% of anxious and depressed patients initially present with somatic instead of psychological symptoms to their primary care physician^20,41 clearly point out the clinical value of the concept. In a recent review on presenting somatization, Garcia-Campayo and Sanz-Carillo⁴² pointed to the stability over time of somatic presentations and somatic attribution style. In light of this, and given the tacit assumption that there may be a continuum between acute somatic presentations in primary care and the chronic forms of somatization described in DSM, future research on presenting somatization should pay attention to treatment outcome studies in addition to naturalistic follow-up studies. These studies may lead to a better understanding of the prognosis of presenting somatization and may enable us to further clarify the relation between somatic presentations and anxiety or depressive disorders, as well as their evolution over time.

Table 1 clearly demonstrates that the concepts related to functional somatization differ from each other with respect to their defining characteristics. It remains unclear, however, what concept can be considered most useful from a clinical and a research perspective. To answer this question, we summarize a number of conclusions regarding the conceptual and methodological issues that we have discussed so far.

First, no clear arguments yet exist to decide on the optimal symptom threshold because most of the functional somatization concepts seem to be predictive of important clinical outcome variables. Second, Simon and Gureje⁵⁷ have clearly demonstrated that it is impossible to measure somatization reliably as a lifetime disorder. As a consequence, current somatic symptoms, followed up prospectively, may be a more appropriate focus for research on somatization than lifetime symptoms. Third, although the existence of several distinct symptom groups has an empirical basis,^63,66,67 it remains unclear to what extent the involvement of different symptom groups is necessary to define a clinically relevant somatization concept. Fourth, in view of the known diversity within the somatizing population,²⁵ the inclusion of specific psychological characteristics as part of the definition of any somatization concept seems premature. Finally, throughout this paper, we have emphasized the necessity to reliably exclude organicity on the basis of objective medical information.

Upon screening each of the concepts described in Table 1, it appears that multisomatoform disorder,⁶ as diagnosed with the PRIME-MD⁵² somatoform module, comes close to meeting the requirements that can be inferred from the above stated conclusions: 1) the symptom threshold is highly predictive of disability, 2) the focus is on current symptomatology, 3) there are no requirements with respect to either the number of symptom groups involved or psychological characteristics, and 4) organicity is excluded on objective grounds. What is probably most appealing about this concept, from both research and clinical perspectives, is the strategy intrinsic to the PRIME-MD. This strategy, combining a self-report schedule with a structured interview, offers the advantage of being less time-consuming without sacrificing the use of medical information, which is crucial to decide whether the symptoms endorsed by the patient are medically explained. A limitation of the concept, especially from a research point of view, is the limited number of symptoms that are included in the patient questionnaire of the PRIME-MD somatoform module, possibly leading to a restriction of range. In addition, the use of a rather low symptom cutoff may produce a somewhat heterogeneous patient population. Finally, the requirement that at least one symptom has been present for at least 2 years reintroduces an element that may be susceptible to inconsistent recall.

One possible way to improve the validity of functional somatization and to clarify its relation to presenting somatization is the use of a multi-axial approach for research purposes. Recent studies of discrete somatoform disorders^69,70 have already pointed out the importance of such an approach. Relevant axes to include are the number of symptoms reported, number and type of organ systems involved, duration of symptoms, degree of associated disability, associated psychopathology, symptom attribution, and specific psychological characteristics. The use of a multi-axial approach should not be an end in itself, however, but rather a means to an end. The objective of such an approach is to integrate different concepts into one instrument to develop more homogeneous concepts of somatization on a solid empirical basis. To this end, the focus should be on prospective studies in the general population and in different medical settings. Ultimately, this research may lead to a more evidence-based treatment of specific groups of somatizing patients.

ACKNOWLEDGMENTS

 
The authors wish to thank Stan Maes, Ph.D. (University of Leiden, The Netherlands), who provided comments on an earlier version of the paper.

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