Decreased Brain Fractional Anisotropy in Schizo-Obsessive Comorbidity

fornix illustration
Researchers collected magnetic resonance imaging that showed that patients with schizo-obsessive comorbidity had extensive cortico-subcortical and perceptual processing-related white matter changes compared with patients have either schizophrenia or obsessive compulsive disorder.

Patients with schizo-obsessive comorbidity show significantly decreased fractional anisotropy of whole-brain white matter and increased radial diffusivity (RD), according to a study published in Schizophrenia Bulletin.

Using tract-based spatial statistics and probabilistic tractography, researchers examined the pattern of white matter abnormalities in patients with schizo-obsessive comorbidity (n=28), patients with schizophrenia (n=28), patients with obsessive-compulsive disorder (OCD) (n=30), and demographically matched healthy controls (n=30). Participants diagnosed with schizo-obsessive comorbidity needed to meet the diagnostic criteria for both schizophrenia and OCD concurrently. The positive and negative syndrome scale was used to assess schizophrenia symptoms in the schizo-obsessive comorbidity and the schizophrenia groups, and the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) was used to assess obsessive-compulsive symptoms in patients with schizo-obsessive comorbidity and OCD.

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Patients with schizo-obsessive comorbidity had a significantly decreased mean fractional anisotropy value of whole-brain white matter (t=-3.66; P <.05) and increased RD values (t=3.17; P <.05) in the right sagittal stratum and left crescent of the fornix/stria terminalis. Compared with patients with schizophrenia, OCD, and healthy controls, patients with schizo-obsessive comorbidity also had changed connection probability in the Default Mode Network, the Subcortical Network, the Attention Network, the Task Control Network, the Visual Network, the Somatosensory Network, and the cerebellum.

Limitations of this study included the relatively small sample size and lack of investigation of cognitive function in patient groups. Researchers cannot rule out the confounding effect of medications, although the results of this study indicate no correlation between antipsychotic dosage and the Y-BOCS score in the schizo-obsessive comorbidity group. The incidence of drug-induced OCD symptoms was not examined, which is a key confounding factor in all prior studies investigating schizo-obsessive comorbidity. The imaging protocol and scanning parameters used in this study did not fit the requirement for neurite orientation dispersion and density imaging analysis for estimating the microstructural complexity of dendrites and axons; researchers in future studies should consider incorporating these novel approaches.

These results remain stable across medication dosages and IQ differences. Extensive cortico-subcortical and perceptual processing-related white matter changes in patients with schizo-obsessive comorbidity may indicate specific superimposed effects and neural adaptation of combined schizophrenia and OCD symptoms. Compared with patients with only schizophrenia or only OCD, the deficits in perception, cognition, emotion, and behavioral control in patients with schizo-obsessive comorbidity support the “double jeopardy” and “disconnection” hypotheses of schizo-obsessive comorbidity.

Wang YM, Yang ZY, Cai XL, et al. Identifying schizo-obsessive comorbidity by tract-based spatial statistics and probabilistic tractography [published online July 29, 2019]. Schizophr Bull. doi: 10.1093/schbul/sbz073