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Should Conversion Disorder Be Reclassified as a Dissociative Disorder in DSM–V?

Received October 19, 2006; revised March 26, 2007; accepted April 2, 2007. From the School of Psychological Science s, Univ. of Manchester, U.K.; the Dept. of Psychology, Univ. of Lund, Sweden; Mental Health Care, Drenthe, Assen, The Netherlands; the Dept. of Psychiatry, Istanbul Univ., Istanbul, Turkey; and the Dept. of Clinical and Health Psychology, Utrecht Univ., Utrecht, The Netherlands. Send correspondence and reprint requests to Richard J. Brown, Ph.D., ClinPsyD, Academic Division of Clinical Psychology, University of Manchester, 2nd Floor, Zochonis Building, Brunswick Street, Manchester, M13 9PL, U.K. e-mail: richard.james.brown{at}manchester.ac.uk
© 2007 The Academy of Psychosomatic Medicine

ABSTRACT

TOP ABSTRACT INTRODUCTION BACKGROUND EVIDENCE SUMMARY CONCLUSIONS AND IMPLICATIONS REFERENCES

 
Pseudoneurological symptoms (i.e., conversion disorder), historically subsumed within the "hysteria" concept alongside phenomena such as psychogenic amnesia and multiple personality disorder, have been classified as somatoform disorders since DSM–III. Since then, there have been repeated calls to reclassify conversion disorder with the dissociative disorders, as in ICD-10. The authors review issues such as the high correlations between pseudoneurological and dissociative symptoms, the high rates of trauma reported for both groups, and the position that these phenomena share underlying processes. Although reintegrating pseudoneurological symptoms with the dissociative disorders is not without complications, there is a strong case for such a reclassification.

INTRODUCTION

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The question of how physical symptoms for which no medical explanation can be found (so-called "medically unexplained symptoms;" [MUS]) should be classified has always been a vexing issue. Successive editions of the Diagnostic and Statistical Manual (DSM) have adopted different schemes for classifying these symptoms, and debate about the most appropriate system continues. The current edition of DSM¹ places these symptoms in the Somatoform Disorders category, with individual subcategories defined by the nature, number, and duration of the symptoms in question (Table 1). According to this system, unexplained deficits in motor or sensory functioning (e.g., paralysis, seizures, sensory loss, gait disturbance) are classified as conversion disorders alongside other MUS within the Somatoform Disorders grouping. An exception is made for patients whose motor or sensory symptoms are part of a broader syndrome characterized by a history of many unexplained symptoms across multiple bodily systems. Many such individuals are more appropriately diagnosed as cases of somatization disorder, which is typically regarded as the definitive example of somatoform illness.

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TABLE 1. Classification of Somatoform Disorders in ICD–10 and DSM–IV

The planning process for DSM–V, which is due for publication in 2011, is already underway, and suggestions abound for how the classification of MUS should be revised.^2,3 A number of commentators have argued that DSM–V should adopt the system used in the 10th Edition of the International Classification of Diseases (ICD-10),⁴ which separates medically unexplained motor and sensory symptoms from the somatoform disorders, classifying them instead as dissociative (conversion) disorders (see Table 2).^2,3,5–9 Because the implications of such a move are potentially far-reaching, this article examines the arguments and evidence for reclassifying conversion disorder as a dissociative disorder in DSM–V.

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TABLE 2. Classification of Dissociative Disorders in ICD–10 and DSM–IV

BACKGROUND

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History
Before DSM, many of the phenomena now encompassed by the Somatoform and Dissociative Disorders categories were captured by the hysteria concept. Janet’s^10,11 influential theory of hysteria assumed that these conditions reflected dissociations among "the systems of ideas and functions that constitute personality (p 332)"¹¹ brought about by a reduction of the individual’s integrative capacity, due to traumatizing events, severe illness, or exhaustion. These ideas pertained to psychobiological complexes (systems) that included thoughts, affects, sensations, behaviors, and memories. Janet’s model was later modified by Breuer and Freud,¹² who argued that the process of dissociation was a psychological defense used by traumatized individuals to protect themselves against overwhelming affects; these affects were then thought to be transformed, or converted, into physical symptoms, allowing them to be expressed without the associated traumatic material becoming conscious. The processes of dissociation and conversion were thought to be responsible for a wide range of symptoms, such as amnesia, fugue, and identity disturbance, as well as a host of medically unexplained physical complaints mimicking both neurological (e.g., paralysis, convulsions, sensory loss) and non-neurological (e.g., nausea, fatigue) illness. At that time, it was assumed that all of these symptoms were produced by similar psychological processes, on the grounds that they tended to co-occur within the same individuals, typically after a history of potentially traumatizing life-events, and were often associated with common features such as high suggestibility and an apparent responsivity to psychological treatment methods like hypnosis.

The first two editions of DSM^13,14 were etiologically driven and heavily influenced by these early approaches to hysteria. DSM–II incorporated a Hysterical Neurosis category, which was further divided into "conversion" and "dissociative" subtypes. The former subtype captured psychogenic deficits in voluntary motor or sensory function, such as paralysis, anesthesias (blindness, deafness, etc.), dyskinesias (tics, tremors, etc.) and the like, whereas the latter encompassed alterations in consciousness or identity, such as fugue and multiple personality. Other MUS were categorized as psychophysiological disorders and were separated from the hysterical neuroses, reflecting the (unsubstantiated) assumption that the former involved structural changes to the underlying bodily system (e.g., hypertension).⁷

Subsequent editions of DSM,^1,15–17 in contrast, adopted a purely descriptive approach to classification, with conditions being grouped together on the basis of prima facie similarities and statistical overlap rather than etiological considerations. The Somatoform Disorders category was introduced on this basis in DSM–III^15,16 to encompass conditions characterized by the presence of symptoms that were suggestive of general-medical illness but were thought to be primarily psychological in origin. Conditions previously categorized within the conversion subtype of hysterical neurosis in DSM–II were reclassified in a Conversion Disorder subcategory of Somatoform Disorders, created to capture symptoms specifically suggestive of neurological illness. Because conditions previously classified within the dissociative subtype of hysterical neurosis were not obviously medical, however, they were divorced from the conversion disorders in DSM–III and categorized alongside other disturbances of memory, perception, and identity in a separate Dissociative Disorders category; this scheme has been maintained in subsequent editions of the Manual. According to DSM–IV, this separation is more practical than conceptual, with the conversion disorders being classified as somatoform simply to emphasize the particular importance of considering and ruling out neurological and other general-medical problems when diagnosing these conditions.¹⁷ By separating the conversion and dissociative disorders, however, the later editions of DSM have created the mistaken impression among clinicians and researchers that the two groups of conditions are unrelated, leading to considerable confusion.

Terminology
Despite the atheoretical stance of recent editions of DSM, the terms "dissociation" and "conversion" are clearly far from theory-neutral. Although they are used largely descriptively in DSM–IV, the terms are often viewed as referring both to a group of psychiatric syndromes and the psychological processes by which those syndromes are brought about. Implicit endorsement for this assumption seems to be provided by the list of criteria for Conversion Disorder in DSM–IV, which states that the symptoms in question must be associated with conflicts, stressors, or other psychological factors, even though the empirical evidence for this association is mixed, at best.^18,19 Clearly, clinicians often encounter patients whose pseudoneurological symptoms are associated with, or appear to have been precipitated by, psychological conflicts; at present, however, there is no research evidence that these conflicts are "transformed" into somatic symptoms, as suggested by the conversion model. Ultimately, the diagnosis of these conditions in clinical practice tends to be based on the nature of the presenting symptoms and the exclusion of possible medical causes, rather than the identification of relevant psychological factors.¹⁹ In the absence of compelling research evidence for the psychological process of conversion, this article uses the descriptive term "pseudoneurological symptoms" to refer to those conditions currently captured by the Conversion Disorders category in DSM–IV, namely deficits in motor or sensory functioning that suggest neurological or other medical illness, but for which no organic explanation has been found. We also include "brief unresponsive states" without a demonstrable organic cause within this category. We use the terms "MUS" and "somatoform symptoms" to refer to the broader category of physical symptoms for which no medical explanation has been found, and which are the primary complaint in patients with somatoform disorders (with the exception of hypochondriasis and body dysmorphic disorder, which do not involve MUS as a defining feature; for this reason, these conditions will not be considered in this review.) The terms "dissociative symptoms" and "dissociative disorders" are used descriptively to refer to the complaints encompassed by the DSM–IV Dissociative Disorders category and/or assessed by measures such as the Dissociative Experiences Scale (DES),²⁰ the Dissociation Questionnaire (DIS–Q),²¹ and the Structured Interview for DSM–IV Dissociative Disorders (SCID–D).²²

Prevalence and Clinical Presentation
Despite claims suggesting the disappearance of conversion disorder,²³ pseudoneurological symptoms are common in both psychiatric and general-medical settings. Up to one-fourth of patients in Western neurological services present with "nonorganic" symptoms,^24,25 and the prevalence may be even higher in some cultures.²⁶ Most, if not all, organic neurological symptoms have a medically-unexplained counterpart, with limb weakness, gait disturbances, abnormal movements, seizures, and sensory disturbances being particularly common. Symptoms of this sort are often associated with high levels of distress, disability, and health-resource utilization, and they are frequently part of a more chronic and complex disorder.²⁷ Patients with pseudoneurological symptoms have overall psychiatric-symptom scores close to those of general psychiatric patients, suggesting high general psychiatric comorbidity.²⁸ In one 2-year follow-up, 89.5% of patients with pseudoneurological symptoms had at least one other psychiatric diagnosis.²⁷

EVIDENCE

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There are two main arguments for moving pseudoneurological symptoms from the Somatoform to the Dissociative Disorders category in DSM–V. First, it has been claimed that the statistical correlation between pseudoneurological and dissociative symptoms is so high that the two may be better regarded as phenomenologically different symptoms of the same underlying syndrome. Second, and relatedly, it is widely held that pseudoneurological and dissociative symptoms involve similar psychological processes. We present evidence pertaining to these two arguments below.

Co-Occurrence of Dissociative, Pseudoneurological, and Other Somatoform Symptoms
Several early clinical case series reported that unexplained neurological symptoms are very common among patients with multiple personality disorder (currently, Dissociative Identity Disorder [or DID] in DSM–IV)..^29–31,32 More recently, a Turkish study found that pseudoneurological symptoms are one of the commonest causes of emergency psychiatric admission in patients with DID and related conditions.³³

Studies using the Dissociative Disorders Interview Schedule (DDIS)³⁴ have also found that MUS are extremely common in patients with DID, many of whom also meet diagnostic criteria for somatization disorder (Table 3).^35–37 Studies using the Somatoform Dissociation Questionnaire (SDQ–20),³⁸ which mostly comprises items pertaining to pseudoneurological phenomena (e.g., anesthesias, seizures, paralysis, dysphagia), have found that these symptoms are significantly more common in patients with dissociative disorders than in psychiatric control subjects and that the severity of these symptoms is also correlated with the complexity of the dissociative disorder (Table 3).^38–42 Symptom ratings on the DDIS and SDQ–20 are based on self-reports, however, and, without medical investigation of the symptoms reported in these studies, it is impossible to tell whether they are comparable to those experienced by patients with diagnosed pseudoneurological disorders.

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TABLE 3. Medically Unexplained Symptoms in Dissociative Disorder Groups

Other studies have measured dissociative symptoms in patients with well-documented pseudoneurological symptoms (Table 4). Using the DDIS, for example, Litwin and Cardeña⁴³ reported that 50% of a sample with medically unexplained seizures would have qualified for a DSM–IV dissociative disorder diagnosis. Similarly, Tezcan and coauthors⁴⁴ and Sar and coworkers²⁷ used the SCID–D to diagnose dissociative disorders in mixed pseudoneurological samples, obtaining prevalence rates of 30.5%⁴⁴ and 47.4%,²⁷ respectively. In the latter study, a concurrent dissociative disorder predicted higher psychiatric comorbidity more generally; these included somatization disorder, dysthymic disorder, major depression, borderline personality disorder, self-destructive behavior, suicide attempts, and childhood trauma.²⁷

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TABLE 4. Dissociative Symptoms in Conversion Disorder Groups

Mixed results have been found in studies using questionnaire measures of dissociation, such as the DES and DIS–Q. Several studies have found significant correlations between the SDQ–20, DES, and DIS–Q,^40,42 whereas others^28,45,46 have reported elevated DES scores in patients with medically unexplained seizures, as compared with control subjects. Other studies with similar populations have failed to find comparable differences, however.^47–49 It is likely that these mixed findings are due to the fact that only some DES and DIS–Q items are related to pseudoneurological illness. According to one recent taxonomy, the DES and DIS–Q include items pertaining to two qualitatively distinct categories of pathological phenomena ("detachment" and "compartmentalization"), with only compartmentalization being directly linked to pseudoneurological symptoms.^50,51 Because the DES and DIS–Q combine detachment and compartmentalization phenomena within a single total score, along with related, but nonpathological, experiences such as absorption, any link between pseudoneurological symptoms and compartmentalization is obscured.^18,50–52 Unfortunately, studies in this area rarely present participants’ scores on meaningful subsets of DES items, such as those on the Dissociative Taxonomy⁵³ or a depersonalization–derealization subscale, which could shed some light on these equivocal findings.

Evidence from several studies demonstrates that patients with pseudoneurological symptoms often experience other MUS. Mace and Trimble,⁵⁴ for example, followed a group of pseudoneurological patients and found that 64% met criteria for somatization disorder 10 years later, even though only 4% had initially received that diagnosis. Similarly, Swartz and collaborators⁵⁵ found that patients with large numbers of MUS across multiple bodily systems had pseudoneurological complaints as their predominant symptoms. Gara and coauthors⁵⁶ also found that patients with pseudoneurological symptoms had numerous symptoms encompassing multiple systems, whereas Interian and collaborators⁵⁷ found that patients with four or more pseudoneurological symptoms had higher levels of psychopathology, disability, and other MUS than patients who did not meet this criterion.

Common Underlying Processes
Clearly, the statistical overlap between pseudoneurological and dissociative symptoms is insufficient in itself to justify their co-classification. Indeed, by this criterion, there would be an argument for classifying pseudoneurological symptoms with other correlated states, such as anxiety and depression, which would be neither meaningful nor useful. If, however, the overlap between dissociative and pseudoneurological symptoms reflects a set of common underlying processes, then the grounds for their co-classification are much stronger.

Following Janet, Breuer, and Freud, several recent theorists have drawn a link between pseudoneurological symptoms and the dissociative disorders,^{6,9,50,58–62} with an abnormal lack of integration between mental modules or systems being regarded as the common underlying feature across these conditions. Dissociative amnesia, for example, is thought to involve a reversible retrieval deficit that prevents memories from being integrated into conscious awareness. There is good evidence that a similar process is responsible for the apparent memory loss associated with many medically unexplained seizures, which can be reversed by use of appropriate hypnotic suggestion.⁶³ Similarly, other studies suggest that patients with medically unexplained sensory loss (e.g., blindness, deafness) process information in the affected modality, but that the results of this processing are temporarily unavailable to conscious awareness because of a lack of integration between implicit and explicit perceptual processes.⁶⁰

Most contemporary theorists assume that potentially traumatizing events are an important predisposing or precipitating factor for many such "dissociated" states and that high suggestibility confers vulnerability to the development of these conditions. Consistent with this, histories of abuse and other forms of potentially traumatizing events are particularly common in dissociative disorder patients^9,32,63–68 as well as those with pseudoneurological symptoms^43,70–72 and other MUS.^27,73–76 Similarly, relatively high levels of hypnotic suggestibility have been found in both dissociative⁷⁸ and pseudoneurological-symptom patients,⁷⁹ although not all studies have found such a relationship with pseudoneurological symptoms.^43,45 There are insufficient data to establish whether high hypnotic suggestibility is found in patients with other MUS.

Although pseudoneurological and dissociative symptoms have recently been viewed as the result of similar dissociations between psychobiological systems (i.e., Janet’s "systems of ideas and functions"), recent theorists have often excluded non-neurological MUS, such as pain, fatigue, dizziness, sexual dysfunction, and so forth, from their models.^60,62 In turn, dissociative and pseudoneurological symptoms are rarely considered in generic reviews and theories of MUS.^80,81 By separating MUS in this way, such theories perpetuate the idea that these phenomena involve different psychological processes. Other recent theories, in contrast, resurrect the 19th-century idea that dissociations between psychobiological systems may be relevant to patients with many different types of MUS, as well as many of the symptoms encompassed within DSM–IV and ICD-10 Dissociative Disorders.^9,58,59 This latter approach is clearly more consistent with the research summarized here.

SUMMARY

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Taken together, these findings provide a relatively consistent picture. Many patients with dissociative disorders report phenomena that are akin to the pseudoneurological symptoms experienced by patients with DSM-defined conversion disorders, as well as many other MUS. Similarly, one-third to one-half of patients with diagnosed pseudoneurological symptoms meet criteria for an additional dissociative disorder. Patients with pseudoneurological symptoms often do not exhibit high scores on measures of dissociation, such as the DES, although we believe this reflects the fact that scores on the DES are derived from items encompassing a wide range of qualitatively distinct phenomena, only some of which are relevant to somatoform and pseudoneurological illness. Indeed, patients with pseudoneurological symptoms typically score high on measures such as the SDQ–20, which is thought to tap the type of dissociation that is most relevant to this group. Many pseudoneurological patients also report histories of other MUS, with pseudoneurological symptoms often being the predominant complaint in patients with the most severe medically unexplained syndromes. There is also a growing body of research and theory suggesting that patients with dissociative and pseudoneurological symptoms both suffer from an abnormal division of psychobiological systems, and have other important features in common, such as histories of abuse and high suggestibility.

CONCLUSIONS AND IMPLICATIONS

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On balance, the frequent co-occurrence of dissociative and pseudoneurological symptoms, their joint classification in ICD-10, and the theoretical and empirical arguments for common underlying mechanisms, provide a strong case for moving pseudoneurological symptoms (i.e., Conversion Disorder) to the Dissociative Disorder category in DSM–V. Such a move would have the advantage of alerting clinicians to the possible presence of symptoms such as amnesia, depersonalization, and identity disturbance in patients with pseudoneurological symptoms (and vice versa) and the importance of considering the trauma histories of these individuals. Grouping pseudoneurological symptoms with the dissociative disorders would also foster a more integrated approach to theory, research, and clinical practice in relation to these conditions. Also, such a move would bring DSM–V in line with the ICD and thereby psychiatric classification, globally. On these grounds, we believe that this is the most effective solution of the available alternatives.

In recommending this reclassification, we recognize a need to distinguish between "genuine" pseudoneurological symptoms and symptoms that appear pseudoneurological but are actually atypical manifestations of other mental disorders. For example, a proportion of symptoms diagnosed as pseudoseizures are likely to be atypical panic attacks, and not dissociative in nature.⁸² Such a distinction is important because the explanation offered to patients and the associated treatment are likely to differ in each case. This distinction clearly has important implications also for the selection of research participants.

The question of whether the term "dissociative" should be used to refer to this expanded group of conditions remains controversial. It could be argued that the term has no place in an atheoretical system such as DSM because it implies allegiance to a particular theoretical model of the conditions in question.⁷ In our view, however, the terms "dissociation" and "dissociative" can be used descriptively to refer to conditions characterized by a pathological separation or division between processing in an affected modality (which is intact) and the individual’s awareness of that processing (which is disturbed). Such a definition makes no assumptions about the specific psychological processes involved in creating or maintaining this separation/division. As such, we believe these terms should be retained in DSM–V.

What effect would the reclassification of pseudoneurological symptoms (i.e., DSM–IV Conversion Disorders) have on the classification of the somatoform disorders more generally? Although the evidence clearly shows that the overlap between the dissociative and pseudoneurological disorders is considerable, the co-occurrence of pseudoneurological illness with other somatoform symptoms is just as impressive. Moreover, there is evidence to suggest that pseudoneurological and other somatoform symptoms have similar psychosocial precipitants (e.g., potentially traumatizing events),⁸³ and there are conceptual grounds for assuming common underlying mechanisms.^9,58,59 Furthermore, pseudoneurological symptoms are an important aspect of somatization disorder, which is regarded by many as the paradigmatic example of a somatoform disorder. Indeed, the most severe cases of somatization disorder appear to be those characterized by numerous pseudoneurological symptoms. It would clearly be unsatisfactory to assume that pseudoneurological symptoms are dissociative disorders when they occur in isolation but somatoform disorders when they occur alongside other MUS. This is particularly true given that many patients with pseudoneurological symptoms often report new MUS over time. How could this situation be resolved?

One possible answer would be to move both Somatization Disorder and pseudoneurological symptoms to the Dissociative Disorder category in DSM–V. Because somatization disorder is regarded as the extreme endpoint on a continuum of somatoform severity, however, and categorical diagnosis is based on an arbitrarily-defined symptom cutoff, would less-severe somatoform conditions also need to be moved to the Dissociative Disorders category? It is difficult to imagine such a suggestion being well received by many somatoform-disorders researchers.

Part of the problem is that the Somatoform Disorders category currently comprises an extremely heterogeneous group of conditions. Even leaving Hypochondriasis and Body Dysmorphic Disorder aside, categories such as Somatization Disorder, Undifferentiated Somatoform Disorder, and Somatoform Pain Disorder capture a wide range of patients, some of whom belong together and some of whom most likely do not. Thus, a patient with circumscribed chronic fatigue syndrome (CFS) probably does not belong in the same category as a patient with severe somatization disorder, whereas a patient who experiences CFS in the context of numerous other functional somatic syndromes probably does.⁸⁴ It may be that dissociative mechanisms are relevant to the latter patient, but not the former. Clearly, further research is required to address these possibilities; studies comparing pseudoneurological symptoms in patients with unifocal and multifocal somatoform disorders may be particularly informative in this respect.

Although the nature and best classification of somatization disorder requires further research and theoretical consideration, our review of the literature strongly suggests that moving pseudoneurological symptoms (i.e., conversion disorder) back to the dissociative fold would make better sense of the empirical database, help conceptual integration of related areas, and, last but not least, finally bring concordance across DSM and ICD taxonomies.

ACKNOWLEDGMENTS

 
The authors are grateful to Jon Stone and two anonymous reviewers for their thoughtful comments on an earlier version of the article.

This article was written by members of the Conversion Workgroup, International Society for the Study of Trauma and Dissociation (ISSTD) Research Planning Committee for DSM–V.

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