Background
Increased peripheral cytokine levels have been observed in patients with psychotic disorders; however, large high-quality studies with individually matched healthy controls have been lacking regarding cytokines in cerebrospinal fluid (CSF) of individuals with psychotic disorders.

Methods
Patients diagnosed with a non-organic, non-affective psychotic disorder (ICD-10: F20/22–29) within a year prior to inclusion and individually age- and sex-matched healthy controls were included by identical in- and exclusion criteria’s except for the psychiatric diagnoses. All participants were aged 18–50 years and individuals with neurological or immunological disorders were excluded. CSF cytokines were analyzed with MesoScale V-PLEX neuroinflammation panel. Co-primary outcomes were CSF interleukin-6 (IL-6) and IL-8.

Results
We included 104 patients and 104 healthy controls, matching on age, sex and BMI. No significant differences were found for the primary outcomes IL-6 (relative mean difference (MD): 0.97, 95 %CI: 0.84–1.11, p = 0.637) or IL-8 (MD: 1.01, 95 %CI: 0.93–1.09, p = 0.895). Secondary analyses found patients to have higher IL-4 (MD: 1.30, 95 %CI: 1.04–1.61, p = 0.018), a trend towards higher IFN-γ (MD: 1.26, 95 %CI: 0.99–1.59, p = 0.056), and lower IL-16 (MD: 0.83, 95 %CI: 0.74–0.94, p = 0.004) than healthy controls, though not significant after correction for multiple testing. IL-8 and IL-16 were found positively associated with CSF white blood cells and CSF/serum albumin ratio. The study was limited by 77.9 % of the patients being on antipsychotic treatment at time of intervention, and that levels of nine of the 26 cytokines were below lower limit of detection (LLOD) in >50 % of samples; however, for the primary outcomes IL-6 and IL-8 more than 99.5 % of the samples were above LLOD and for IL-8 all samples exceeded the lower limit of quantification (LLOQ).

Conclusions
We found no evidence of increased IL-6 and IL-8 in patients with recent-onset psychotic disorders in contrary to previous findings in meta-analyses of CSF cytokines. Secondary analyses found indication of higher IL-4, decreased IL-16, and borderline increased IFN-γ in patients, neither of which have previously been reported on in CSF analyses of individuals with psychotic disorders.