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. Can J Psychiatry. 2009;54(7):452-459. Clinical Implications * Family history of bipolar affective disorder and frequent switching of antidepressants, indicating an inadequate response to treatment in patients with depression presenting at a young age, can be helpful to clinicians as guidance for identification of those at high risk for a bipolar course. * The distinction carries a therapeutic implication as delayed or inappropriate treatment may precipitate poorer outcomes. * Close monitoring of the high-risk group may therefore be necessary. Limitations * This is a retrospective study and data collection was based on retrospective review of case records, which might have been incomplete. * The severity of various depressive and anxiety domains could not be accurately quantified retrospectively. Only clinical parameters with numerical values and the presence or absence were routinely documented in case records were used for comparison and statistical analysis. Key Words: Chinese, unipolar depression, bipolar depression, manic switch, structured clinical interview for the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition axis I disorders, sex, age at presentation, antidepressants, family history Abbreviations used in this article AD antidepressant BD bipolar disorder PYNEH Pamela Youde Nethersole Eastern Hospital SCID 1 Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition SSRI selective serotonin reuptake inhibitor There is evidence that the distinction between major depressive disorder and BD is a therapeutic imperative. Treatments for the 2 disorders are substantially different and treating patients having BD with unipolar therapy algorithms may lead to unfavourable outcomes. ADs may induce manic or hypomanic swings or cycle acceleration.1 Depression is often the first manifestation of abnormal mood in BD. In a survey2 of 500 patients, 33% reported depressive symptoms as the most common initial symptom. In addition, although manic episodes are the distinguishing diagnostic feature of BD, on average BD I patients spend 3-fold as much time in a depressed state than in a manic or hypomanic state.3 Longitudinal studies have shown that conversion from unipolar to BD is not uncommon. …