MICROSTRUCTURAL CHANGES IN FRONTAL WHITE MATTER ASSOCIATED WITH CANNABIS USE IN EARLY PHASE PSYCHOSIS: A DIFFUSION TENSOR IMAGING (DTI) STUDY
Introduction: This project aimed to examine the impact of cannabis use on the brain white matter (WM) tissue abnormalities associated with psychosis, in individuals at the early phase of psychosis (< 5 years from diagnosis). Using diffusion tensor imaging (DTI), it was predicted that there would be evidence of WM disruption in patients with psychosis compared to healthy controls, and more so in patients with earlier and heavier lifetime cannabis use. Methods: The primary outcome measure was fractional anisotropy (FA) which reflects WM integrity. There were two groups of subjects: 1) Patients with early phase psychosis and 2) Healthy controls with no cannabis use. Scans were acquired on a 1.5T MRI and imaging analysis was done both within a volume of interest (VOI - left superior longitudinal fasciculus) and at the full-brain level. Results: A trend level decrease in mean VOI FA was found in patients relative to healthy controls, but no difference was found at the full-brain level. Within the patient group, there was a significant positive correlation found between cumulative lifetime cannabis use and mean VOI FA (but not mean full-brain FA), however there was no relationship between age of onset of cannabis use and mean FA either at the full-brain level or within the VOI. Discussion: There was trend level evidence of WM abnormalities in the VOI (but not at the full-brain level) in patients at the early phase of psychosis. Furthermore, contrary to what was hypothesized, there was evidence of increased WM integrity in patients with heavier lifetime cannabis use within the VOI. By accounting for concomitant alcohol and substance use, this study provides novel insight about WM microstructure, as it relates to early phase psychosis and adolescent cannabis use.