White Matter Microstructure and Gray Matter Volume in Cannabis-Induced Psychosis and Schizophrenia With Cannabis Use.

Objective: This study explored the differences in white matter (WM) microstructural integrity and gray matter (GM) volume between cannabis-induced psychosis (CIP) and schizophrenia with cannabis use (SZC).

Methods: This cross-sectional study with convenience sampling involved three groups of 20 participants each (CIP, SZC, and a control group without substance use), matched on age, handedness, and education. CIP and SZC were diagnosed with the Psychiatric Research Interview for Substance and Mental Disorders. Diffusion tensor and kurtosis imaging were done, and fractional anisotropy (FA), mean diffusivity, and mean kurtosis were estimated. GM volume was measured with voxel-based morphometry.

Results: Group comparisons revealed comparable age at initiation and duration and frequency of cannabis use between participants in the SZC and CIP groups. Participants with SZC had lower FA than controls in the anterior and retrolenticular internal capsule limbs, cingulate gyrus hippocampal formation, fornix, and superior fronto-occipital fasciculus (all p<0.05). Participants with CIP had lower FA than controls in the left fornix and right superior fronto-occipital fasciculus but higher FA than those with SZC in the left corticospinal tract (all p<0.05). On morphometry, participants with CIP had greater cerebellar GM volume than those with SZC and greater inferior frontal gyrus volumes than controls (all p<0.05).

Conclusions: Widespread WM microstructural abnormalities were observed in participants with SZC, and fewer but significant WM disruptions were observed in those with CIP. Better WM integrity in some WM fiber tracts and greater GM volumes in crucial brain areas among those with CIP may have prevented the transition to schizophrenia.