Are Schizophrenic disorders with or without early cannabis use neurobiologically distinct disease entities? A meta-analysis of magnetic resonance imaging studies.

Cannabis use is considered an important risk factor for the development of psychotic illness and is associated with worse outcomes of the disorder. This study aimed to determine through a meta-analytic approach whether patients at the onset of schizophrenia with comorbid cannabis use (SCH CU+) show a different pattern of brain abnormalities as compared to patients with no comorbid cannabis use (SCH CU-). Ten Magnetic Resonance Imaging (MRI) studies were identified as suitable for analysis leading to the inclusion of n= 465 patients with schizophrenia (n= 227 SCH CU+ and n= 238 SCH CU-) and n= 366 healthy controls. Compared to healthy controls, both SCH CU+ and SCH CU- patients showed reduction of whole brain, total grey matter and hippocampal volumes. The direct comparison of SCH CU+ and SCH CU- patients, including up to 5 independent studies, did not demonstrate significant differences of brain volumes between the two groups even though total and regional grey matter volume deficits were more prominent in SCH CU+ patients. The available literature data indicate that, essentially, there is an overlap of brain abnormalities in SCH CU+ and SCH CU- patients at the onset of schizophrenia. The common vs specific trajectories of brain pathomorphology in SCH CU+ and SCH CU- patients are discussed.