Neuronal Integrity and Suicidality in Bipolar Depression: a Diffusion Tensor Imaging Study

Bipolar disorder is a chronic mood disorder which is characterized by repetitive episodes, usually manifests through adolescence or early adulthood. It has a prevalence of approximately 2,5% with a 1:1 ratio of male and female. It is a disorder that may disrupt central nervous system functions such as cognition, thought, perception, affect, judgement, adaptation to the environment and behavioural regulation. It may manifest with various clinical onsets. Although etiology of bipolar disorder is still unknown, some biological factors such as BDNF, oxidative stress and structural changes of brain are proven to have a role in etiology.

Diffusion tensor magnetic resonance imaging (DTI) is a neuroimaging technique that elucidates abnormalities of brain white matter (WM), based on structural investigation of a tissue via measurement of diffusion rate and direction of water molecules. This method lets imaging of white matter tracts, whole anatomical extent and structural integrity of the brain tissue. So, it can provide data about anatomical connectivity of brain. There are some parameters used for indicating microstructural integrity of white mat-ter such as fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in DTI. FA is a measure which reflects directional coherence of water diffusion, and it is sen¬sitive to microstructural WM differences. It is defined on a scale ranging from mostly isotro¬pic (when approaching to zero) indicating poor integrity of the axons to mostly anisotropic (when approaching to 1) indicating intact WM integrity. ADC is a scalar index of the rate of water diffusion among different dif¬fusion directions under a Gaussian distribution. A higher value of ADC indicates lesser restricted diffusion, and it implies fewer organized structures in WM which supports presence of abnormalities in the structural in¬tegrity of white matter. As it has a complicated literature, in this study, we aimed to investigate neuronal integrity and its abnormalities by DTI, which may contribute to the etiology of bipolar depression.