Transdiagnostic investigation of white matter integrity and cortical thickness in cognitive subgroups within the schizophrenia-bipolar spectrum

Abstract

Background: Cognitive deficits are cardinal features of schizophrenia-spectrum disorders (SSD) and bipolar disorder (BD). However, their heterogeneous and overlapping characteristics require a dimensional approach to better understand the neurobiological basis of cognition in the psychosis spectrum. To date, only a few studies have examined the neuroanatomical features of cognitive subgroups in transdiagnostic samples, and white matter microstructural characteristics of these subgroups have not been elucidated. This study aimed to investigate white matter and cortical thickness alterations in cognitive subgroups in the schizophrenia-bipolar spectrum. Methods: Globally Impaired (n = 31) and Near-Normal (n = 28) cognitive subgroups, comprising individuals diagnosed with schizophrenia (SZ), schizoaffective disorder (SAD) or BD, and healthy controls (HCs, n = 29), underwent 3T T1-weighted structural magnetic resonance imaging and diffusion tensor imaging scanning. Fractional anisotropy and cortical thickness measures were compared between the cognitive subgroups and healthy controls. Results: Abnormalities in white matter microstructure were only observed in patients with global cognitive impairment compared to HCs. The Near-Normal subgroup did not differ from HCs in white matter integrity. A bilateral reduction in cortical thickness was observed in both the Globally Impaired and Near-Normal subgroups when compared to HCs. Cortical thickness measures did not differentiate between the cognitive subgroups. Conclusions: While reductions in cortical thickness in frontal and temporal regions appear to be a common feature of SZ and BD, abnormalities in white matter microstructure are associated with global cognitive impairment in the schizophrenia-bipolar spectrum. These original findings may be important in identifying more biologically valid clinical syndromes within the schizophrenia-bipolar spectrum.