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White matter changes in early phase schizophrenia and cannabis use: an update and systematic review of diffusion
Jacob Cookey1, Denise Bernier1, Philip G Tibbo1
1Department of Psychiatry, Dalhousie University, 5909 Veterans' Memorial Lane, 8th Floor, Rm. 8206 Abbie J. Lane Memorial Building, QEII Health Sciences Centre, Halifax, NS, Canada, B3H 2E2; Capital District Health Authority, Room 3030, 3rd Floor, AJLB, 5909 Veterans' Memorial Lane, Halifax, NS, Canada, B3H 2E2.
Objectives:
The impact of cannabis use on the brain tissue is still unclear, both in the healthy developing brain and in people with schizophrenia. The focus of this review is on white matter, the primary connective infrastructure of the brain.
Methods:
We systematically reviewed diffusion tensor imaging (DTI) studies of early phase schizophrenia (illness effect), of cannabis use in otherwise healthy brains (drug effect), and of early phase schizophrenia with cannabis use (combined effects). Studies had to include a healthy, non-cannabis using, control group as well as report on fractional anisotropy as it is the most commonly used DTI index. We excluded cohorts with heavy alcohol or illicit drug use and studies with a sample size of less than 20 in the clinical group.
Results:
We retained 17 studies of early phase schizophrenia, which together indicate deficits in white matter integrity observed in all fiber tract families, but most frequently in association, callosal and projection fibers. In otherwise healthy cannabis users (2 studies), deficits in white matter tracts were reported mainly in callosal fibers, but also in projection and limbic fibers. In cannabis users with early phase schizophrenia (1 study), deficits in white matter integrity were also observed in all fiber tract families, except for limbic fibers.
Conclusions:
The current literature points to several families of white matter tracts being differentially affected in early phase schizophrenia. Further work is required to reveal the impact of cannabis use in otherwise healthy people as well as those with schizophrenia.
Limitations:
Paucity of available studies as well as restricting analysis to FA values represent the main limitations of this review.