Department of General Practice and Nursing Home Medicine, Leiden University Medical Centre
Department of Psychiatry, Leiden University Medical Centre, Leiden, The Netherlands
Correspondence: M.W.M. de Waal, LUMC Department of General Practice and Nursing Home Medicine, PO Box 2088, 2301 CB Leiden, The Netherlands. Tel: +31 71 5275318; fax: +31 71 5275325; e-mail: M.W.M.de_Waal{at}lumc.nl
See editorial, pp.
465467, this
issue.
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ABSTRACT |
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Aims To quantify the prevalence of, and functional impairment associated with, somatoform disorders, and their comorbidity with anxiety/depressive disorders.
Method Two-stage prevalence study: a set of questionnaires was completed by 1046 consecutive patients of general practitioners (aged 2580 years), followed by a standardised diagnostic interview (SCAN 2.1).
Results The prevalence of somatoform disorders was 16.1% (95% CI12.819.4). When disorders with only mild impairment were included, the prevalence increased to 21.9%. Comorbidity of somatoform disorders and anxiety/depressive disorders was 3.3 times more likely than expected by chance. In patients with comorbid disorders, physical symptoms, depressive symptoms and functional limitations were additive.
Conclusions Our findings underline the importance of a comprehensive diagnostic approach to psychiatric disorders in general practice.
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INTRODUCTION |
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METHOD |
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Setting
The study took place in eight university-affiliated general practices in
The Netherlands. The age and gender distributions are comparable to those of
the Dutch population. The electronic medical records of all patients were
available through the central database (Registratie Netwerk Universitaire
Huisartspraktijken Leiden En Omstreken (RNUH-LEO)) of the family practice
registration network of Leiden (13 practices). The database contains
diagnostic codings according to the International Classification of Primary
Care (ICPC; Lamberts & Wood,
1990) for each consultation.
Patients
Between April 2000 and December 2001 a sample of 1778 attendees, aged
2580 years, was sent the screening questionnaires by mail. After 2
weeks those who had not responded were sent a reminder, including the
questionnaires. For each general practice the sample consisted of all
consecutive patients on 1330 arbitrary days within a 3-month period. To
avoid problems with language, the study was limited to Dutch natives. Patients
were not included if they were unable to participate in an interview because
of difficulties such as deafness, aphasia or cognitive impairment. A total of
1046 patients (59%) returned the questionnaire and indicated that they were
willing to participate. Data from the RNUH-LEO database allowed fairly
detailed analyses of non-response characteristics. Non-response analyses
showed that male patients of 2544 years of age in particular were less
willing to participate (response of 46%). When comparing reasons for
consultation in the 3 months prior to selection, non-responders did not have
more psychological problems (ICPC classification chapter P: 14%) than
responders but they did have slightly more social problems (ICPC
classification chapter Z: 7% v. 4%). Approximately 50% of both
non-responders and responders consulted a general practitioner five or more
times in the year prior to selection. Logistic regression modelling showed
that after correction for age and gender (which both still have a significant
effect) the only other variable with a significant effect was a social reason
for encounter (odds ratio=0.6). Social problems are mainly problems in the
relationship with a partner or other, mourning and problems related to the
work situation.
Questionnaires
Participants completed the SF36 functional limitation questionnaire
(Aaronson et al, 1998)
as a measure of functional impairment, the Hospital Anxiety and Depression
Scale (HADS; Zigmond & Snaith,
1983) as a measure of anxiety and depression and the Physical
Symptom Checklist (PSC; available from the authors on request) to quantify the
number of reported physical symptoms.
The first two questionnaires have been validated extensively and described sufficiently elsewhere. In general medical out-patients the total HADS scale has been validated for detecting psychiatric disorders: a cut-off point of 15 gave a sensitivity of 74% and a specificity of 84% (Spinhoven et al, 1997). The PSC is a checklist of 55 physical symptoms that were mentioned in the DSMIII classification (American Psychiatric Association, 1980) and includes a broad array of symptoms covering most organ systems. The presence of symptoms is rated on a severity scale of 03 for the preceding week. A symptom is rated as present for scores 2 and 3. The total score represents the sum of the number of symptoms that are endorsed. In previous studies physical symptoms were a useful severity indicator of somatoform disorders and a fair predictor of medical utilisation (Van Hemert et al, 1993; Kroenke et al, 1994; Speckens et al, 1996).
High-risk sample
A total score of 15 or more on the HADS or a score of 5 or more on the PSC
defined the high-risk sample, which is 48% of the total sample. Of the 506
high-risk patients, 190 patients screened positive on both the HADS and the
PSC, 265 patients screened positive only on the PSC and 51 patients screened
positive only on the HADS. The choice of instruments and cut-off values for
the high-risk sample are somewhat arbitrary because a sample of low-risk
patients was interviewed as well. The procedure merely aimed at increasing the
number of interview positives for a subsequent treatment study without
affecting the prevalence estimate.
Diagnostic interview
Of all the high-risk patients, 80% (404/506) participated in the diagnostic
interview. Of the 540 low-risk patients, 15% were invited for diagnostic
interview and 84% (69/82) participated. We tried several times to contact
non-responders by mail or by telephone. Non-responders to the diagnostic
interview were somewhat younger and scored 1.5 points higher on the HADS
anxiety sub-scale (possible range 021): no differences were found in
the number of physical symptoms or functional impairment (SF36
sub-scales).
The Schedules for Clinical Assessment in Neuropsychiatry (SCAN 2.1; World Health Organization, 1999) were used by World Health Organization-certified psychologists for the psychiatric diagnostic interviews. Throughout the study we held regular sessions with the interviewers to maintain diagnostic standards. During the interview patients were asked about concurrent physical illnesses, and the interviewers made the clinical decision on whether symptoms were unexplained or not. The researcher (I.A.A.) supervised all interviews for medical diagnostic data. Whenever necessary, medical diagnostic data concerning symptoms were obtained from the individual general practitioners. When doubt remained, the symptom was regarded as explained. The scoring algorithm needed to be modified slightly to allow separate and accurate diagnoses of hypochondriasis and somatisation disorder according to the criteria of DSMIV. The modifications were reported to the World Health Organization task force that is developing the SCAN. Because the overlap between somatoform disorders and anxiety and depressive disorders is the object of this study, hierarchical rules between these disorders were not applied. Within the DSMIV chapters the hierarchical rules were preserved. All chronic somatoform disorders were diagnosed (duration of at least 6 months): both acute pain disorder and somatoform disorder not otherwise specified were excluded.
An important modification of DSMIV (compared with its predecessors) is that a severity criterion of significant clinical distress or functional impairment has been included in most Axis I disorders. The distinction between Axis I and Axis V has become blurred. From a clinical point of view this modification is well justified, but from an epidemiological point of view the modification introduces an element of subjectivity in the diagnostic process and comparisons with previous studies may have become hampered. We took meticulous care to rate this item separately for each diagnosis throughout all interviews. To analyse the influence of this criterion, the prevalence rates were re-analysed using all criteria of symptoms and duration, with the exception of the severity criterion.
Analyses
Of the 404 high-risk patients interviewed, 116 had a DSMIV
somatoform disorder, 40 had an anxiety disorder and 34 had a depressive
disorder. Of the 69 low-risk patients, 3 had a somatoform disorder and 1 had
an anxiety disorder. All prevalence estimates and confidence limits were
weighted for the sampling procedure
(Cochran, 1997). To quantify
the overlap of somatoform disorders and anxiety and/or depressive disorders,
the weighted prevalence and confidence limits for the combinations are given.
In addition, we calculated the ratio that represents the factor by which
comorbidity exceeds chance expectations: by taking the observed prevalence and
dividing it by the prevalence expected by chance. Analyses were conducted
using SPSS for Windows 11.0 and MsExcell 97 software.
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RESULTS |
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The age and gender distributions of the prevalence figures are summarised in Table 2. The estimated prevalence of somatoform disorders was much lower in patients aged 65 years and over. The same was found for anxiety disorders and depressive disorders. Women tended to have more somatoform disorders (no significant difference). We found no gender differences for anxiety disorders. Depressive disorders were slightly but not significantly more prevalent in females.
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Comorbidity and functional impairment
The comorbidity of DSMIV somatoform disorders and anxiety or
depressive disorders is considerable (Fig.
1). The observed comorbidity of somatoform disorders and
anxiety/depressive disorders was 4.2% (95% CI 2.95.5). The expected
percentage of comorbidity occurring only by chance was 1.3% (95% CI
1.97.2). The observed/expected ratio was 3.3 (95% CI 1.86.1). Of
all patients with a somatoform disorder, 26% (95% CI 2328) also had an
anxiety and/or depressive disorder: 17% (95% CI 1223) had an anxiety
disorder and 17% (95% CI 1223) had a depressive disorder. Of all
patients with an anxiety and/or depressive disorder, 54% (95% CI 4860)
also had a somatoform disorder.
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The symptoms and functional limitations of patients with a somatoform disorder together with an anxiety or depressive disorder are more severe: they add up when comorbidity is present (Table 3). In comparison with patients without disorders, the rating on the PSC was 5.1 (95% CI 28) points higher for patients who only had an anxiety or depressive disorder and 5.4 (95% CI 47) points higher for patients who only had a somatoform disorder. For the patients with comorbid somatoform and anxiety or depressive disorders the rating was 10.2 points higher (95% CI 713), which approximately equals the sum of the increase due to the separate categories. The same applied to the HADS depression scale, whose rating increased by 4.8, 2.2 and 6.9 points, respectively. For the HADS anxiety scale the increase in rating in the subgroup with comorbid disorders (6.5) was less than the sum of the increase in the separate subgroups (5.9 and 2.7, respectively). Functional impairment according to the SF36 showed a different pattern for somatoform compared with anxiety or depressive disorders. In comparison with patients without psychiatric diagnoses, patients with only anxiety or depressive disorders were most severely limited in their social functioning and in their role functioning because of emotional problems. Patients who only had somatoform disorders were limited in all areas covered by the SF36. Patients with comorbid disorders were more limited in all areas, and when compared with patients with only somatoform disorders their scores were significantly worse for social functioning, role functioning because of emotional problems and subjective health.
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DISCUSSION |
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Strengths and weaknesses of the study
This is a comprehensive study of the prevalence of strictly defined
DSMIV somato-form disorders, anxiety disorders and depressive disorders
in a consulting general practice population, with special emphasis on
functional impairment.
The 59% response rate, although not uncommon in primary care, was fairly low for a prevalence study. Selectivity of the responding sample could, in theory, invalidate our prevalence estimates. We addressed this issue with a detailed nonresponse analysis using registered data from the RNUH-LEO database. The response selection was independent of frequency of consultation and of psychological problems, as seen by the general practitioner. Response was comparatively low in the younger males (46%). If they were the healthier subjects, this may have resulted in some overestimation of disorders. On the other hand, social problems were slightly underrepresented in the responding sample, which could have affected the rates towards some underestimation.
The exclusion of somatic disorders as a potential explanation of symptoms is one of the unsolved problems in studies of somato-form disorders. Some form of clinical judgement will have to be involved. In the present study we adopted a cautious approach. The interviewers and the supervising general practitioner made an initial judgement of information provided by the patients. If there was any doubt about the possibility of a somatic disorder as an explanation of the presenting symptoms, additional information was sought from the general practitioner treating the patient. When doubt remained over whether a diagnosis of somatoform disorders was justified, the symptom was regarded as explained. This may have resulted in an underestimation of the prevalence of somatoform disorders.
Prevalence estimates
When comparing our study with previous prevalence studies, our estimates
are relatively low. For DSMIV somatoform disorders a prevalence
estimate of 30% has been found (Fink
et al, 1999). For current depressive disorders previous
prevalence estimates were 8% (DSMIV;
Olfson et al, 1997),
11.126% (DSMIIIR;
Coyne et al, 1994;
Linzer et al, 1996;
Tiemens et al 1996)
and 11.7% (ICD10; Sartorius et
al, 1996). Prevalence estimates for current anxiety disorders
were 11.6% (DSMIV; Olfson et
al, 1997), 14.418% (DSMIIIR;
Coyne et al, 1994;
Linzer et al, 1996;
Tiemens et al, 1996)
and 10.2% (ICD10; Sartorius et
al, 1996). Prevalences rather resembled the rates found in
community surveys, for example in Italy
(Faravelli et al,
1997) and The Netherlands (Bijl
et al, 1998).
Our lower estimates are most likely due to our strict definition of the disorders. The SCAN interview is known as a high-threshold diagnostic interview with a comparatively strong emphasis on clinically relevant symptoms (Simon et al, 1995; Brugha et al, 2001). In addition, we took meticulous care to rate the criterion of functional impairment that was introduced in most Axis I disorders in the update from DSMIIIR to DSMIV. It has been demonstrated recently that adherence to clinical significance criteria may reduce the prevalence estimates of anxiety and depressive disorders by approximately one-third (Narrow et al, 2002). Another explanation for our low estimates could be found in the use of psychotropic medication, which may vary between populations. It is theoretically possible that the prevalence rates could be reduced by 50% or more in a population with optimal treatment. So far, other studies have not reported any figures concerning psychotropic treatment.
Surprisingly, no differences were found by gender for prevalence rates of anxiety disorders, and gender differences for depressive disorders were minimal. This could be due to limited statistical power, because confidence limits, especially in men, were rather large. Another possibility is that our emphasis on impairment contributed to this finding. For depressive disorders (but not for anxiety disorders) the gender differences increased when the DSMIV criterion of moderate to severe clinical impairment was ignored.
Comorbidity
A high comorbidity of somatoform disorders and anxiety or depressive
disorders has been a common finding in previous studies
(Barsky et al, 1992; Ormel et al, 1994;
Escobar et al, 1998;
Maier & Falkai, 1999). Functional somatic syndromes are also related to (but not fully dependent on)
anxiety and depression (Henningsen et
al, 2003).
Kroenke et al (1997) showed that anxiety disorders, depressive disorders, multi-somatoform disorder and somatoform disorder not otherwise specified have independent effects on functional limitations. This study confirms that the symptoms and functional limitations of the disorders can be summated, with the most prevalent somatoform disorders in the present study being undifferentiated somatoform disorder. Patients who have anxiety or depressive disorders are particularly limited in social functioning, role functioning because of emotional problems and subjective health. Patients with somatoform disorders are limited in all areas that are measured by the SF36. In patients with comorbidity the impairments are summated.
Implications of the study
The findings on comorbidity have implications for the focus of treatment.
To engage patients in treatment it is of primary importance to distinguish
clearly whether the patient initially presents with psychological or physical
symptoms. Patients with a somatoform presentation tend to attribute their
symptoms primarily to a physical disorder. The initial motivation for
treatment of psychological symptoms will be limited. To engage subjects in a
psychologically oriented treatment the somatoform presentation of symptoms
should be recognised and dealt with
(Sharpe et al, 1996;
Kroenke & Swindle, 2000).
Patients might accept that psychological distress is a consequence of
persistent somatic symptoms, or that the relationship is circular (symptoms
lead to distress, which, in turn, exacerbates the symptoms).
With DSMV on the horizon, discussion again has started about the classification of somatoform disorders (Wise & Birket-Smith, 2002). It has been argued that somatoform disorders are not psychiatric disorders in a strict sense. Indeed, it is not very clear that unexplained physical symptoms are caused by psychological factors. It is clear, however, that there is a strong relationship with anxiety and depression, given that half of the patients in general practice with anxiety or depression suffer from a somatoform disorder as well. The relationship could be due to anxiety and depression causing (awareness of) physical symptoms, or physical symptoms causing anxiety and depression, or there may be a more complex relationship such as a circular causality. Furthermore, a third factor, such as consulting behaviour, could be related to both. In addition to patients with comorbid disorders, many more patients suffer from a somatoform disorder without anxiety or depression. From our study it is evident that both somatoform disorders and anxiety and depression come with substantial functional impairment and that the combination is even worse. A somatoform presentation seems to result from a complex interplay of perception and attribution of symptoms, resulting in unproductive illness behaviour. It has been demonstrated repeatedly that a cognitivebehavioural approach can be effective in alleviating this burden (Kroenke & Swindle, 2000). The inclusion of a well-defined category of somatoform disorders in DSMV is needed to facilitate further research on the effective treatment of such patients.
Burden of illness and primary care
Somatoform disorders have a major impact on the burden of psychiatric
illness. At least one out of six patients seen by a general practitioner has a
somatoform disorder. Furthermore, our findings demonstrate that when
somatoform disorders occur in combination with anxiety or depressive
disorders, symptoms and impairments can be summated. To engage patients in an
effective psychological treatment it is important to recognise the somatoform
presentation of symptoms. General practitioners should have a strong working
knowledge of the principles of diagnosis and treatment of somatoform
disorders, as well as of anxiety and depressive disorders.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication June 2, 2003. Revision received September 29, 2003. Accepted for publication November 3, 2003.
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