Bipolar Disorder

Bipolar disorder (BD) is a complex and severe mental illness, associated with substantial morbidity and increased mortality. Depressive symptoms frequently prevail in the course of illness, and significant morbidity arises from acute affective episodes and subacute states. Phenotypically, unipolar and bipolar depression seem to share several clinical features, which leads to an average delay of 10 years between initial symptoms and the diagnosis of BD. Multidimensional approaches have been proposed to better predict BD in at-risk populations; however, the differential diagnosis between these two entities remains a clinical challenge. Similarly to other chronic conditions, it has been proposed that BD is also a progressive disorder, where multiple affective episodes may result in structural, functional, and neurobiological brain abnormalities that accelerate illness progression, with subsequent treatment resistance and reduction in interepisode interval. Therefore, strategies to improve diagnosis accuracy are pivotal to improve clinical outcomes and long-term prognosis in the course of BD. In this chapter, we aim to provide a critical overview of psychopathological, sociodemographic, and neurobiological features to help clinicians properly distinguish unipolar and bipolar depression. Pathological and therapeutic implications of misdiagnosing BD are briefly discussed.