A total of 1487 patients treated for MDD were consecutively examined in 13 mental health centers in China. The patients' socio-demographic and clinical characteristics were recorded using a standardized protocol and data collection procedure. The HCL-32 was self-completed by patients to identify hypomanic symptoms, and the MINI was used by clinicians to establish DSM-IV diagnoses.
The proportions of undiagnosed BD (all types), BD-I and BD-II were 20.8%, 7.9%and 12.8%, respectively. The HCL-32 had low positive predictive value (0.43). Compared to MDD patients without subthreshold manic features, MDD patients with subthreshold manic features were younger at onset, less likely to be married and had more depressive episodes on a seasonal basis, and more frequent depressive episodes overall. Compared to BD patients, MDD patients with subthreshold manic features had an older age at onset and less frequent depressive episodes and less family history of psychiatric disorders, appetite, weight gain and time spent sleeping, suicide ideation and attempts and psychotic symptoms.
At least one fifth of Chinese patients treated for MDD may have an undiagnosed BD. The HCL-32 is useful to identify broader subthreshold bipolar features. The findings need to be confirmed by longitudinal studies using more comprehensive, standardized instruments.