| Summary: | After prolonged psychostimulant abuse, some individuals develop transient psychotic symptoms referred to as “substance induced psychosis” (SIP), which closely resemble the symptoms observed in schizophrenia spectrum disorders. The comparability in psychotic presentation between SIP and the schizophrenias suggests that similar underlying neural deficits may contribute to the emergence of psychosis across these disorders. Anatomically, only a small number of studies have attempted to characterize the structural alterations in SIP – all of which solely focus on methamphetamine associated psychosis. To further characterize the nature of psychostimulant-associated psychosis, three investigations were performed to identify 1) gray matter abnormalities, 2) white matter abnormalities, and 3) environmental risk factors of current symptom severity in psychostimulant dependent individuals with and without a DSM-IV diagnosis of substance-induced psychosis. To investigate gray matter abnormalities in study 1, a voxel-based analysis of magnetic resonance images (MRI) was performed between a group of 74 cocaine dependent nonpsychotic (CDN) individuals and a group of 29 individuals with cocaine-associated psychosis (CAP). The CAP group had significantly smaller volumes of the thalamus and left hippocampus, controlling for age, total brain volume, current methamphetamine dependence, and current marijuana dependence.
To investigate white matter abnormalities in study 2, diffusion tensor imaging was employed in a group of individuals with cocaine-associated psychosis (CAP; n=24) and a cocaine dependent nonpsychotic group (CDN; n=43). Tract based spatial statistics (TBSS) was used to investigate group-differences in white matter diffusion parameters. The cocaine-associated psychosis group showed significantly lower fractional anisotropy values than the cocaine dependent nonpsychotic group (p<0.05) in voxels within white matter tracts of fronto-temporal, fronto-thalamic, and interhemispheric pathways. In study 3, environmental risk factors were used to predict current positive and negative psychotic symptom severity in a sample of 171 individuals meeting DSM-IV-TR criteria for psychostimulant dependence. Increased severity of current positive psychotic symptoms was significantly related to increased frequency of methamphetamine and marijuana use in the past 28 days, and methadone-abstinence. Collectively, these results begin to characterize structural alterations in the expression of psychostimulant associated psychosis – the nature of which suggests there may be shared neuroanatomical correlates in the expression of different forms of psychosis. === Medicine, Faculty of === Graduate
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