Cerebrospinal fluid (CSF) levels of interleukin-6 (IL-6) are significantly increased in patients with schizophrenia and major depressive disorder, Japanese study results show.
In contrast, serum IL-6 levels were not increased in either of the two diagnostic groups.
"Increased CSF IL-6 levels in both patients with schizophrenia and those with MDD suggest that inflammatory mediators may be commonly involved in the pathogenesis of these disorders," comment Hiroshi Kunugi (National Center of Neurology and Psychiatry, Tokyo) and team.
The researchers assessed levels of IL-6 in CSF and blood drawn from 32 patients with schizophrenia, 30 with MDD, and 35 mentally healthy controls.
There were no significant differences among the groups regarding mean age, gender distribution, or body mass index, although the prevalence of smoking was higher in both patient groups compared to controls.
The team found that patients with schizophrenia and those with MDD had significantly higher CSF levels of IL-6 than controls.
However, there were no significant differences between the groups regarding serum levels of IL-6.
Furthermore, there was no significant correlation between CSF and serum IL-6 levels in any of the groups.
Overall, IL-6 levels were significantly higher in CSF than in serum. However, when analyzed separately in each diagnostic group, the difference between CSF and serum IL-6 levels was significant only in patients with schizophrenia.
There was no significant correlation between CSF IL-6 levels and antipsychotic dosage or Positive and Negative Syndrome Scale (PANSS) scores in patients with schizophrenia. Similarly, CSF IL-6 levels did not significantly correlate with antidepressant dose or Hamilton Depression Rating Scale-21 (HAMD-21) scores in MDD patients.
When only nonsmokers were compared, patients with schizophrenia had significantly higher CSF IL-6 levels compared with controls, but the difference between MDD patients and controls was not significant.
Kunugi et al conclude in the Journal of Psychiatric Research: "The present findings suggest that IL-6 of central origin is associated with the pathophysiology of these disorders."
They add: "The lack of significant correlation with PANSS or HAMD-21 scores suggests that IL-6 levels are not greatly influenced by the severity of the symptoms. However, further studies with a longitudinal design are required to investigate how CSF IL-6 levels change during the course of the disease."
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