The bipolar diathesis of treatment-resistant major depressive disorder.

Objective. In this study, we determined the prevalence of bipolarity in patients with treatment-resistant depression (TRD) by investigating demographic and clinical characteristics, diagnostic subtypes and illness outcome of patients with resistant depression. Methods. A medical record review of patients who were admitted to a university hospital with the diagnosis of major depressive disorder (MDD) was conducted. DSM-IV diagnoses at the index hospitalization and 6 months after discharge and detailed clinical information were obtained. We categorized subjects into a TRD group or a non-TRD group and re-evaluated the patients using the criteria for bipolar spectrum disorders. Results. There were 281 patients diagnosed with MDD. At discharge, the number of patients who fulfilled the criteria for BSD was higher in the TRD group (47.1%) than in the non-TRD group (3.8%) (P<0.001). At the end of the 6-month follow-up period, the diagnoses of 38 patients were changed; 18 (26.5%) of the TRD group were subsequently classified as having a bipolar disorder, as were seven (3.3%) in the non-TRD group (P<0.001). There was no difference between these two groups for other clinical and demographic variables. Conclusion. The findings of this study suggest that many patients with TRD have a bipolar diathesis.