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Q Does ICD-10 classification of mild, moderate, and severe depression predict risk of relapse and suicide in people hospitalised with their first depressive episode?
All psychiatric hospitals in Denmark; enrolment January 1994 to December 1999.
The national Danish Psychiatric Register records all psychiatric admissions for the Danish population (5.3 million people). During the enrolment period, 7199 people were diagnosed with a single mild, moderate, or severe depressive episode according to ICD-10 criteria (mild, 1103 people; moderate, 3182 people; severe, 2914 people). Temporary discharge and readmission within 3 days was counted as a single depressive episode.
Mild, moderate, or severe depressive episodes (ICD-10 criteria).
Risk of relapse; risk of death.
Follow up period:
From 1 day to 6 years.
ICD-10 criteria predicted that people with severe depression were more likely to relapse or commit suicide than people with milder depression (median time to relapse: 6.1 years with mild depression; 5.5 years with moderate depression; 3.2 years with severe depression; risk of suicide: 0.5% with mild depression; 1.0% with moderate depression; 2.0% with severe depression; see table⇓).
ICD-10 categorisation of mild, moderate, and severe depression predicts the risk of relapse and suicide in people diagnosed by their first depressive episode.
Diagnoses were not validated, and as data relate to people hospitalised for depression, they may not be generalisable to the general population.
This is a further example of what can be achieved with national databases such as those which researchers in Denmark have had access to for a number of years. By using the ICD-10 categorisation of the severity of depression of mild, moderate, and severe, which was introduced to Denmark in 1994, Kessing has extended the work of Hoyer et al,1 also from Denmark, who examined patients admitted to hospital with affective disorders between 1973 and 1993. Kessing has demonstrated elegantly what clinicians have believed: that the risk of relapse of depression and the risk of suicide increase with increasing degrees of depression. It was also apparent that those with more severe depression were more likely to attract a subsequent diagnosis of bipolar disorder or schizophrenia.
This research is limited by the fact that these subjects would have had a significant degree of depression to be admitted, and it is probably fair to state that admission practices may vary not only from country to country, but within countries, and they may have changed considerably in the last decade with the focus on ambulatory care. Treatments are also not documented, and one cannot necessarily extrapolate the results to other countries.
Nevertheless, this research highlights the utility of such national databases, as it shows well the clinical value of a dimensional diagnostic approach to depression. Furthermore, it adds substance to the suggestions of Paykel2 that the severity criteria should remain in the International Classification of Diseases, and that they could profitably be incorporated into revisions of the American Psychiatric Association Diagnostic and Statistical Manual.
From the clinician’s point of view, it is reassuring to have data confirming the need to focus particularly on the severely depressed, while keeping an open mind about the possibility that a bipolar or schizophrenic disorder may be emerging in those patients.
For correspondence: Lars Kessing, Department of Psychiatry, University of Copenhagen, Rigshospitalet, Blegdamsvej, Copenhagen, Denmark;
Sources of funding: the Stanley Medical Research Institute and the Lundbeck Foundation.