Unipolar mania: a distinct disorder?

Background: This study aimed to identify the differences between unipolar mania and classical bipolar disorder. Methods: Patients with at least four manic episodes and at least 4 years of follow-up without any depressive episodes were classified as unipolar mania. This group was compared to other bipolar-I patients defined according to DSM-IV regarding their clinical and socio-demographic variables. Results: The rate for unipolar mania as defined by the study criteria was found to be 16.3% in the whole group of bipolar-I patients. Unipolar manic patients tended to have more psychotic features and be less responsive to lithium prophylaxis compared to other bipolar-I patients. Limitations: Because it was a retrospective study, there may be some minor depressive episodes left unrecorded in the unipolar mania group despite careful and thorough investigation. In addition, even with our fairly strict criteria for the diagnosis of unipolar mania, the possibility of a future depressive episode cannot be excluded. Conclusions: Unipolar mania may be the presentation of a nosologically distinct entity.