Rudolf Magnus Institute of Neuroscience, Department of Psychiatry, University Medical Centre, Utrecht
Parnassia Psycho Medical Centre, The Hague
Centre for Biostatistics, Utrecht University
Rudolf Magnus Institute of Neuroscience, Department of Psychiatry, University Medical Centre, Utrecht, The Netherlands
Correspondence: Dr Natalie D. Veen, Department of Psychiatry (A 00.241), University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands. Tel: +31 30 250 8180; e-mail: n.veen{at}psych.azu.nl
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ABSTRACT |
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Aims To determine diagnostic stability in a Dutch population-based psychosis incidence cohort, to examine the frequencies of diagnostic shifts to and from schizophrenic disorders and to report the revised relative risks of schizophrenic disorders for immigrants.
Method A 30-month follow-up study assessed the cohort (n=181) by means of face-to-face diagnostic interviews.
Results Diagnostic stability of schizophrenic disorders was high (91%), but lower for other psychotic disorders. At follow-up, the initial diagnosis was adjusted to schizophrenic disorder more often than that the reverse occurred. Almost half (49%) of the patients who were not initially diagnosed as having a schizophrenic disorder received this diagnosis at follow-up. The relative risks for most immigrant groups were stable.
Conclusions Schizophrenic disorders are underdiagnosed, rather than overdiagnosed, at first presentation.
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INTRODUCTION |
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METHOD |
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Follow-up study
Two and a half years (mean 30.2 months, s.d.=3.7) after the first contact
the patients were approached for a repetition of the diagnostic assessments.
The resident in psychiatry (N.D.V.) interviewed the patients using a follow-up
version of the CASH (CASHUP; Ho
et al, 1998) and obtained information from the treating
physician and the patient's medical file. The research nurse collected key
data from informants using the IRAOSUP, a modified version of the
IRAOS. If necessary, an interpreter assisted in the administration of
interviews to participants who were not native Dutch speakers. As in the
earlier study, the researchers used all available information to compile a
history, omitting the initial diagnosis and the patient's ethnicity. The
procedure of the diagnostic meeting was identical to that of the incidence
study. J.-P.S. participated in all of the meetings of both the incidence and
follow-up studies.
Three members of the original cohort could not be traced, two had died,
seven refused to participate in the follow-up study, and one had insufficient
information in her medical file. Thus, for 168 participants there was
sufficient information available on which to base a diagnosis at the second
assessment. For 99 patients information was available from three sources
(CASHUP, IRAOSUP and the medical file), for 40 patients
information was available from CASHUP and the medical file, for 5
patients information was available from IRAOSUP and the medical file,
and for 24 patients information was available from the medical file and the
treating physician. It was not possible to obtain key-informant data for 64
patients; in 25 of these patients this was due to lack of family or friends.
There was no association between the number of data sources used and
diagnostic stability (2-test, P=0.39).
Definition of immigrant groups
Four groups of immigrants were delineated: those from Morocco, Surinam,
Turkey and other countries. First-generation (i.e. those not born in The
Netherlands) and second-generation (Dutch-born) immigrants were combined into
one group. People born in The Netherlands and whose parents were born in The
Netherlands are referred to as native Dutch.
Data analysis
Diagnostic stability
Diagnostic stability was defined as the proportion of patients whose
diagnosis at follow-up was in the same main category as in the incidence
study. Four main categories were delineated:
The diagnostic stabilities of brief psychotic disorders and schizophreniform disorders were evaluated separately.
Diagnostic shift towards and away from schizophrenic disorders
The diagnostic shift away from schizophrenic disorders to any of the other
diagnostic main categories was evaluated and compared with the shift in the
reverse direction, using McNemar's test for paired proportions. These
diagnostic shifts were also evaluated for different sections of the
population.
Incidence and relative risks of schizophrenic disorders
To calculate the incidence of schizophrenic disorders and the relative
risks for immigrant groups, data were combined for the patients who had
received this diagnosis at follow-up (n=125) and for the 8 patients
who had received this diagnosis at the initial assessment but could not be
assessed in the follow-up. The incidence after exclusion of the 36 patients
who were not admitted to hospital early in the course of their disorder was
also calculated. For the crude incidence rate, the number of cases was divided
by the number of person-years at risk (same denominator as in the incidence
study). This rate was standardised by direct standardisation for age and
gender to the Dutch population on 1 January 1998. In order to compute 95%
confidence intervals a Poisson distribution was assumed
(MacMahon & Trichopoulous,
1996). Age-adjusted relative risks for schizophrenic disorders in
immigrant groups, by gender and generation, were computed with Poisson
regression analysis using EGRET (Cytel Software, Cambridge, MA, USA).
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RESULTS |
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Diagnostic shifts towards and away from schizophrenic disorders
In Table 2 the diagnostic
shifts to and from schizophrenic disorders is shown for the native Dutch and
immigrant groups. Of the 67 patients who were initially not diagnosed with a
schizophrenic disorder about half (n=33) received this diagnosis at
the follow-up assessment. The diagnostic shift from any other diagnosis to the
main category of schizophrenic disorders occurred significantly more often
than the shift from schizophrenic disorders to any other diagnosis (33
v. 9 patients; McNemar's test Z=12.6, P<0.001).
In all sections of the population there was an increase in schizophrenic
disorders, except in the Surinamese group, where the diagnostic shift to and
from schizophrenic disorder was the same (n=3 each way). For Turkish
immigrants the increase was especially marked, with the diagnosis of 6 of 10
patients being changed to a schizophrenic disorder at follow-up and none of
the previous diagnoses of schizophrenic disorder being changed to another
diagnosis. Owing to the small size of the groups, it was not appropriate to
test for differences between the groups.
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Incidence rates of schizophrenic disorders
The revised crude annual incidence rate of schizophrenic disorders in The
Hague was 2.6 (95% CI 1.83.7) per 10 000. The difference between the
crude and the standardised incidence rates was minimal. The annual crude
incidence rate after exclusion of the 36 patients who were not hospitallised
early in the course of their disorder was 1.9 (95% CI 1.52.3) per 10
000.
Relative risks for immigrant groups
Table 3 shows the (5-year)
age-adjusted relative risks for schizophrenic disorders in immigrant groups,
by gender and generation. For almost all groups there was little difference
from the risks reported in our earlier study. An exception is the revised
relative risk for Turkish-born men, which was found to be significantly
increased.
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DISCUSSION |
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Interpretation of diagnostic shifts
There are different sources of diagnostic instability, which include
subject variance (true changes in the patient), information variance (e.g.
more information available at the follow-up assessment), observation variance
(different interpretations of same stimuli) and criterion variance (e.g. two
observers use different criteria for diagnosing a delusion)
(Spitzer et al,
1975). In order to reduce observation and criterion variance, we
used similar diagnostic instruments at both assessments, the same procedures
at the diagnostic meetings and the same criteria for classification. However,
a limitation of the study was that the diagnosticians at the follow-up
assessment were not masked to the purpose of the study. Most new
cases of schizophrenic disorder at follow-up had received the diagnosis
psychotic disorder not otherwise specified at baseline, a
diagnosis that was often made because the information was insufficient for a
specific diagnosis. Consequently, a likely explanation for many diagnostic
shifts is that the patient (or a relative) disclosed more information
pertinent to the schizophrenia syndrome after the initial assessment. This
might also explain the relatively high rates of diagnostic shift to
schizophrenic disorder for Turkish and Moroccan immigrants. At the initial
assessment the researchers sometimes had difficulties in gathering sufficient
information from those who did not speak Dutch.
A second explanation for diagnostic changes is that they were necessitated by true changes in the clinical picture. One patient, for example, was initially diagnosed with a bipolar disorder on account of a depressive and a manic episode with mood-congruent psychotic symptoms. During the follow-up period, however, his mood was normal but he suffered from acoustic hallucinations and negative symptoms.
Implications
One clinical implication of this study is that the use of an extensive
diagnostic protocol makes it possible to diagnose schizophrenic disorders
reliably at their first presentation. This is important because early
treatment and psycho-education of patients and their families may improve the
course of the disorder (Lieberman &
Fenton, 2000; Malla et
al, 2002). Moreover, physicians should be aware that even if
a patient with a first episode of psychosis is diagnosed as having a disorder
other than a schizophrenic disorder, there is a distinct possibility that this
diagnosis will be adjusted to a schizophrenic disorder at a later date. It is
therefore important that these patients are not lost from sight.
There are also implications for research. First, studies on risk factors and course of schizophrenic disorders should include all patients with a first psychotic episode and not only those initially given a diagnosis of schizophrenic disorder. Second, first-contact rates constitute an underestimation of the true incidence rates. The revised annual incidence rate of schizophrenic disorders was 2.6 per 10 000, compared with 2.1 (95% CI 1.72.5) per 10 000 obtained in the incidence study. The changes in relative risks for immigrant groups were small.
Comparison with earlier reports
We replicated the main results of the Nottingham study. Amin et al
(1999) and Harrison et
al (1999) used similar
methods and found a diagnostic stability of 83% for DSMIIIR
schizophrenia after 3 years, with no significant differences between natives
and immigrants from the Caribbean. Goater et al
(1999) carried out similar
research in London and also reported no significant association between
ethnicity and diagnostic stability. Other studies in this field included only
hospitalised patients, and none compared natives with immigrants (e.g.
Tsuang et al, 1981; Fennig et al, 1994;
Rabinowitz et al,
1994; Chen et al,
1996; Schwartz et al,
2000; Forrester et al,
2001).
Strengths of the study
The strengths of this study lie in its population-based design and the
extensive diagnostic procedures, including direct patient interviews and
direct key-informant interviews at initial and follow-up evaluations. The
cohort was large, and enough information was available to enable a reliable
follow-up diagnosis to be made for 93% of the original cohort. Finally, the
diagnosis was made by psychiatrists who were masked to ethnicity and the
previous diagnosis.
In conclusion, the study's findings indicate that at first presentation, underdiagnosis of schizophrenic disorders is more frequent than overdiagnosis.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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REFERENCES |
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Received for publication November 24, 2003. Revision received June 10, 2004. Accepted for publication July 9, 2004.