White matter changes in early phase schizophrenia and cannabis use: an update and systematic review of diffusion tensor imaging studies.
OBJECTIVE
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.


CONCLUSIONS
Paucity of available studies as well as restricting analysis to FA values represent the main limitations of this review.
Department 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.
Jacob
J
Cookey
Department 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.
Denise
D
Bernier
Department 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. Electronic address: phil.tibbo@cdha.nshealth.ca.
Philip G
PG
Tibbo
D001921:Brain / Q000187:drug effects* / Q000254:growth & development / Q000473:pathology*; D002188:Cannabis / Q000009:adverse effects*; D056324:Diffusion Tensor Imaging; D006801:Humans; D008385:Marijuana Smoking; D009413:Nerve Fibers, Myelinated / Q000187:drug effects / Q000473:pathology; D012559:Schizophrenia / Q000473:pathology*; D066127:White Matter / Q000187:drug effects* / Q000473:pathology*
Cannabis; Diffusion tensor imaging; Early phase schizophrenia; White matter