Diagnostic conversion from depression to bipolar disorders: results of a long-term prospective study of hospital admissions.

Abstract

To analyse the time course and some risk factors for a diagnostic change from major depression to bipolar disorders (BP) over an average of 20 years from the onset of the disorders.
Patients (406) with major mood disorders hospitalised at some time between 1959 and 1963 were followed-up until 1985. The analysis also included the course prior to hospitalisation. Survival analyses and Cox regression models were applied.
A diagnostic change from depression to bipolar I occurred in about 1% of the patients per year and to bipolar II disorders in about 0.5% per year. Risk factors for a change from depression to BP-I disorder were male sex and an early onset of the disorder; risk factors for a change from depression to BP-II disorder were female sex, a later onset of the disorder and a positive family history of mania.
Across the entire lifetime, every new episode of depression brings a new risk for mania; more than half of our severe mood disorder cases became bipolars. The risk of depression developing into bipolar disorder remains constant lifelong.
The diagnostic classification of ICD-9 met RDC criteria for bipolar disorder in only 90% of cases. Part of the data collected in retrospect may be less reliable; the prospective data were only collected every 5 years from 1965 to 1985 using multiple sources; mild manifestations between the follow-ups may have been partially missed. The sample of subsequent hospital admissions for major depression and mania represents a severe group of patients and generalisations to ambulatory cases may not be possible. Not all risk factors for diagnostic conversion described in the literature could be assessed in this study.