A Case-Control Study of Bipolar Depression, Compared with Unipolar Depression, in a Regional Hospital in Hong Kong

Objective: To determine the characteristics of diagnostic conversion from unipolar depression to bipolar depression in psychiatric outpatients, and to compare the profiles of the 2 groups of patients. Method: This is a case–control study in which outpatients newly diagnosed with unipolar depression were reviewed. Outpatients who had polarity conversion to bipolar depression were recruited as subjects and control subjects were matched. The diagnostic validity was enhanced by clinical interview, review of case records by an independent specialist psychiatrist, and administration of the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Axis I Disorders. Multivariate conditional logistic regression was carried out to identify the predictors of bipolar switch. Results: Eighty-eight subjects among those who maintained regular outpatient clinic follow-up ( n = 823) showed bipolar switch during the period under study. The incidence of polarity conversion was 10.7%. Bipolar switch was associated with family history of bipolar affective disorder, use of 3 or more different types of antidepressants in the first 5 years after presentation, an earlier age at presentation of depressive symptoms of less than 37 years, and males. Conclusions: Change in diagnostic polarity is not uncommon in Chinese psychiatric outpatients initially presenting with unipolar depression. They share some common risk factors as identified in Western studies. These can be helpful to clinicians as guidance for identification of patients with depression at high risk for a bipolar course.