Department of Psychiatry, University of Copenhagen (Department of Psychiatry, Rigshospitalet, Blegdamsvej 9, DK 2100 Copenhagen Ø, Denmark. Tel: 3545 6237; fax: 3545 6218; e-mail: lars.kessing{at}rh.dk) and Department of Psychiatric Demography, University of Aarhus, Risskov, Denmark
Funding detailed in Acknowledgements.
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ABSTRACT |
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Aims To validate the ICD-10 categorisation of severity of depression by estimating its predictive ability on the course of illness and suicidal outcome.
Method All psychiatric in-patients in Denmark who had received a diagnosis of a single depressive episode at their first discharge between 1994 and 1999 were identified. The risk of relapse and the risk of suicide were compared for patients discharged with an ICD-10 diagnosis of a single mild, moderate or severe depressive episode.
Results At their first discharge, 1103 patients had an ICD-10 diagnosis of mild depressive episode, 3182 had a diagnosis of moderate depressive episode and 2914 had a diagnosis of severe depressive episode. The risk of relapse and the risk of suicide were significantly different for the three types of depression - increasing from mild to moderate to severe depressive episode.
Conclusions The ICD-10 way of grading severity is clinically useful and should be preserved in future versions.
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INTRODUCTION |
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The aim of our study was to investigate whether the ICD-10 categorisation into diagnoses of mild, moderate and severe depression at discharge from first admission predicted the risk of relapse and eventual suicide. As in prior studies (e.g. Kessing, 1998; Kessing et al, 1998) we used the Danish Psychiatric Central Register as our database, with survival statistics to estimate the risk of relapse and suicide.
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METHOD |
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Study sample
The study sample was defined as consisting of all patients admitted during
the day or overnight to a psychiatric hospital who had a diagnosis of a single
depressive episode (ICD-10, code F32.0-32.3) in a period from 1 January 1994
to 31 December 1999 at the time of their first discharge. The sample was
divided into three groups according to whether the depressive episode was mild
(codes F32.0, 32.00, 32.01), moderate (codes F32.1, 32.10, 32.11) or severe
(codes F32.2, 32.3, 32.30, 32.31). It is well known that some patients are
temporarily discharged to other wards for somatic diagnosis or treatment and
are subsequently readmitted to the psychiatric ward for further treatment of
depression. Since the aim of the investigation was to study relapse, the two
admissions were counted as one episode if readmission occurred within 3 days
of discharge. Patients were therefore not at risk of relapse until 3 days
after discharge: relapse was thus defined as readmission after being
discharged for 3 days. Time to relapse was estimated, censoring if death had
occurred or if relapse had not occurred before 31 December 1999.
In the estimations of time to suicide, patients might have been readmitted several times before suicide or before the end of the observation period. Consequently, patients might have a different diagnosis at subsequent discharges. According to the diagnostic hierarchy in ICD-10, patients who were given a main diagnosis of organic disorder (code F00-09), schizophrenia and related disorders (F20-29) or bipolar disorder (F31) at later discharges were included in the analysis until this diagnostic alteration and thereafter censored from further analysis, since from this point these patients were no longer considered as suffering from a primary depressive disorder. The follow-up period varied between 1 day and 6 years.
Statistical analysis
The Kaplan-Meier method for estimation with censored observations was used
for calculating the probability of remaining discharged and the probability of
not dying by suicide, and the log rank test was used to estimate the
differences between mild, moderate and severe depression
(Kaplan & Meier, 1958).
Cox's regression models were used to adjust for differences in age and gender
at first discharge. The Statistical Package for the Social Sciences was used
(SPSS, 2001).
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RESULTS |
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The risk of relapse in the three patient groups increased with increasing
severity of depression at first discharge
(Fig. 1). Table 2 compares the median
times to relapse for the three groups, and a log rank test showed that the
risk of relapse for the groups differed significantly (2=84.2,
d.f.=2, P<0.0001). Adjusting for differences in age and gender
between the three groups in a Cox's regression model revealed that patients
with a moderate depressive episode at first discharge had a 1.2 (95% CI
1.1-1.4) times greater risk of relapse compared with patients with a mild
depressive episode at first discharge; similarly, patients with a severe
depressive episode had a 1.7 (95% CI 1.5-1.9) times greater risk of relapse
compared with patients with a mild depressive episode. Women had 1.14 (95% CI
1.05-1.25) times increased risk of relapse compared with men, and older
patients at first discharge had less risk of relapse: 0.993 per year of age
(95% CI 0.991-0.995).
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The risk of suicide during the 6 years of follow-up increased with the
severity of depression at first discharge
(Fig. 2), and a log rank test
showed that the differences were significant
(Table 3;
2=13.7, d.f.=2, P=0.001). Cox's regression analyses
with adjustment for differences in age and gender revealed that the risk of
suicide was 1.5 (95% CI 0.6-3.6) times greater in patients with a moderate
rather than a mild depressive episode at first discharge and 2.1 (95% CI
0.9-5.1) times greater in patients with a severe rather than a mild depressive
episode at first discharge. Both confidence intervals included 0, but maximum
likelihood analyses revealed a significant difference between a model with
severity included and a model without (
2=512, d.f.=2,
P<0.0001). Men had 2.2 (95% CI 1.4-3.7) times the risk of suicide
compared with women; however, no significant effect was found for age: 1.008
(95% CI 0.994-1.022).
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DISCUSSION |
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The validity of our results is strengthened by our findings of the usual predictors of relapse and suicide. Thus, women had greater risk of relapse, in accordance with most studies (Angst, 1981; Winokur et al, 1993; Kessing, 1998), and men had a greater risk of suicide, as is well known from prior studies (Cantor, 2000). It should be emphasised that the study concerns only patients with depressive episodes severe enough to lead to hospitalisation, and it is possible that the findings cannot be generalised, for example to primary care patients. Further, the study had a naturalistic approach: patients might have received treatment following discharge and the treatment would have been at the discretion of the responsible clinician, not directed by the researcher. The Danish Psychiatric Central Register contains no data on treatment.
The advantages of our study are that it comprised an observation period of 6 years for the whole Danish population, which is ethnically and socially homogeneous and has a low migration rate. Psychiatric care is well developed, so that people with depression can easily come into contact with a psychiatric hospital. Because all psychiatric in-patient treatment in Denmark is free of charge and there are no private psychiatric in-patient facilities, the study is not biased by socio-economic differences.
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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 March 14, 2003. Revision received June 16, 2003. Accepted for publication July 1, 2003.
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