Predominant polarity and hippocampal subfield volumes in Bipolar disorders

Objectives: Predominant polarity (PP) is a proposed course specifier for bipolar disorders (BD) based on patient lifetime mood episodes. Hippocampal subfield volumetric changes have been proposed as a neurobiological marker for BD and could be influenced by mood episodes. Our study aimed to test the hypothesis that patients with BD differ in hippocampal subfield volumes according to their PP. Methods: We assessed 172 outpatients, diagnosed with BD according to DSM-IV-TR criteria, and 150 healthy control (HC) participants. High-resolution magnetic resonance imaging was performed on all subjects and volumes of all hippocampal subfields were measured using FreeSurfer. Results: Patients with depressive PP (BD-DP) and with uncertain PP (BD-UP) but not with manic/hypomanic PP (BD-MP) showed a global reduction on all hippocampal subfield volumes with respect to HCs. When directly compared, BD-DP presented with smaller bilateral presubiculum/subiculum volumes than BD-MP. Conclusions: Results support the potential utility of PP not only as a clinical but also as a neurobiological specifier of BD.