Clinical features of differential diagnosis between unipolar and bipolar depression in a drug-free sample of young adults

Introduction: Subjects with bipolar disorder suffering of a depressive episode are frequently misdiagnosed as unipolar depression, being important studies assessing the differential diagnosis between bipolar and unipolar depression. Objective: To assess the sociodemographic and clinical features of drug-free young adults in a depressive episode of bipolar or unipolar disorder in order to identify factors that may differentiate these psychiatric conditions. Methods: This is a cross-sectional study with 241 young adults aged between 18 and 29 years who were evaluated using the Structured Clinical Interview for DSM-IV (SCID). The sample comprised patients with BD (n = 89) and major depressive disorder (n = 152), experiencing a depressive episode and not using psychoactive drugs or illicit psychoactive substances. Results: The characteristics associated with bipolar depression were being male (p < 0.001), with a family history of BD (p = 0.013), a higher frequency of childhood traumatic experiences (p = 0.001), younger age of onset of mood disorder (p = 0.004), many previous depressive episodes (p = 0.027), greater severity of depressive symptoms (p < 0.001) and day/night reversal (p = 0.013). Those with unipolar depression showed a higher frequency of biological rhythm disturbances (p < 0.001), and diurnal preference (p = 0.028). Limitations: The sample has not included subjects with severe suicide risk, a possible important marker in differentiate unipolar from bipolar depression. Conclusion: Some clinical aspects may contribute to an early differential diagnosis of both bipolar and unipolar depression even in the initial stages of the disease.