Investigation of peripheral markers of inflammation in patients with different diagnoses on the psychosis spectrum: an observational cross-sectional study

Abstract Background Increasing evidence suggests that inflammatory dysfunction may be important across the psychotic spectrum. In this study, we investigated whether there is a difference between different diagnostic groups, in which psychosis is the common pathway, and healthy controls in markers of peripheral inflammation, such as platelet-lymphocyte ratio (PLR), neutrophil–lymphocyte ratio (NLR), systemic inflammatory response index (SIRI) and systemic immune-inflammatory index (SII), determined by haemogram. Our hypotheses are as follows: patients with a common history of psychosis but with different diagnoses have higher severity of peripheral inflammation compared to healthy controls, regardless of the specific diagnosis. In addition, the severity of peripheral inflammation is similar across different diagnoses across the psychosis spectrum. Results Before and after correction for age and sex, there was no statistically significant difference in PLR between the groups. However, a substantial statistical difference in NLR and SIRI was observed between the groups. According to the post hoc analysis performed to determine which groups the difference was between, schizophrenia and the healthy control group, schizoaffective disorder and the healthy control group, and autism spectrum disorder and the healthy control group differed in terms of NLR; there was only a significant difference in SIRI between autism spectrum disorder and the healthy control group. In addition, there was a statistically significant difference between groups for SII before and after correction for age and sex; however, when paired groups were evaluated using post hoc analysis, no statistically significant differences were found between any two groups. When comparing disorder groups within the psychotic spectrum, it was observed that PLR, NLR, SIRI, and SII levels were comparable. Conclusions Our results showed that several disorders including schizophrenia, schizoaffective disorder and autistic spectrum disorder, with different diagnoses but similarities in terms of a history of psychosis, had increased inflammation compared to healthy controls. This study contributes to the psychosis spectrum approach in that there was no statistically significant difference in the severity of inflammation in disorder groups with a history of psychosis but with different diagnostic categories. However, further research is needed to completely understand the psychosis spectrum, as bipolar disorder patients have similar inflammation levels to those without mental disorders.