Comparison of neurotrophic factors, inflammatory markers, and neurocognition between schizophrenia and bipolar disorder patients with and without psychotic features

Introduction and Objective: The psychosis continuum in bipolar disorder has been a long-debated topic among researchers. To determine the level of differentiation and overlap between schizophrenia and bipolar disorder, a comparative study was planned that considers Schneider's first-rank symptoms, examining neurotrophic factors, inflammatory markers, and neurocognitive functions. The aim of this study is to compare the two disorders, which have previously been examined for genetic associations, in terms of neurotrophic factor levels and neurocognitive functions, and to identify etiological models and developmental differences. Materials and Methods: The study included 30 patients with bipolar disorder with psychotic features, 30 patients with bipolar disorder without psychotic features, 30 patients with schizophrenia, and 30 healthy controls, all diagnosed according to DSM-5 criteria. The Hamilton Depression Rating Scale (HAM-D) and Young Mania Rating Scale (YMRS) were administered to patients with bipolar disorder, and the Positive and Negative Syndrome Scale (PANSS) was used for schizophrenia patients, with only those meeting remission criteria included in the study. Participants underwent a neuropsychological test battery lasting 60-90 minutes to assess cognitive functions, and serum samples were analyzed using the Enzyme-Linked Immuno Sorbent Assay (ELISA) method. Results: In terms of cognitive functions, processing speed, verbal learning, and immediate recall were found to significantly differentiate the patient groups. Cognitive impairment was more pronounced in schizophrenia compared to bipolar disorder. Between patients with psychotic and non-psychotic bipolar disorder, cognitive impairment differed quantitatively rather than qualitatively. Schizophrenia patients had significantly higher CRP and FGF-2 levels compared to non-psychotic bipolar disorder patients. Regarding BDNF levels, patients with psychotic bipolar disorder showed significantly higher values compared to those with schizophrenia and non-psychotic bipolar disorder. Conclusion: It is suggested that elevated CRP and FGF-2 levels may be predictive of psychosis. Larger-scale studies in this area will provide important contributions to the literature. Keywords: Schizophrenia, bipolar disorder, neurocognitive functions, neurotrophic factors, neuroinflammation