CHICAGO— Heavy use of marijuana may put adolescents who are genetically predisposed to schizophrenia at greater risk for the disease, according to Manzar Ashtari, PhD, Sanjiv Kumra, MD, and colleagues.

The investigators used diffusion tensor imaging (DTI) to examine the arcuate fasciculus, a bundle of fibers connecting Broca’s area in the left frontal lobe and Wernicke’s area in the left temporal lobe of the brain. "Unlike MRI, which provides a static picture of brain structures, DTI detects and measures the motion of water molecules in the brain, which can reveal microscopic abnormalities," Dr. Ashtari explained at the 2005 Annual Meeting of the Radiological Society of North America.

The researchers found that repeated exposure to marijuana was related to abnormalities in the development of this fiber pathway, which is associated with the higher aspects of language and auditory functions. "Because this language/auditory pathway continues to develop during adolescence, it is most susceptible to the neurotoxins introduced into the body through marijuana use," said Dr. Ashtari, Associate Professor of Radiology and Psychiatry at Albert Einstein College of Medicine, Bronx, New York.

During the study, DTI was performed on 12 healthy, early-adolescent males compared with 12 late-adolescent males, to show normal human brain development; 11 patients with schizophrenia were compared with 17 matched controls; 15 patients with schizophrenia who smoked marijuana were compared with 17 matched controls; and 15 marijuana smokers were compared with 15 matched non–drug users. The scans revealed no abnormal developmental changes in the language pathway in the healthy adolescents but showed abnormalities in both the patients who smoked marijuana and those with schizophrenia.

"These findings suggest that in addition to interfering with normal brain development, heavy marijuana use in adolescents may also lead to an earlier onset of schizophrenia in individuals who are genetically predisposed to the disorder," said Dr. Kumra, Assistant Professor of Psychiatry at Albert Einstein College of Medicine.

Drs. Ashtari and Kumra said that longitudinal studies are needed to determine whether these alterations in the brain are permanent or change over time. "It is also important to mention that at this time, DTI and MRI are not diagnostic tools for patients with schizophrenia or marijuana smokers," they noted.

Suggested Reading
Di Forti M, Murray RM. Cannabis consumption and risk of developing schizophrenia: myth or reality? Epidemiol Psichiatr Soc. 2005;14:184-187.

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