Interleukin 6 in cerebrospinal fluid of patients with meningitis is not a useful diagnostic marker in the differential diagnosis of meningitis

We assayed interleukin 6 (IL-6) concentrations in cerebrospinal fluid (CSF) from patients affected by meningitis of different aetiologies, and verified whether IL-6 can be used as a diagnostic marker in the differential diagnosis of meningitis. We used a monoclonal antibody enzyme immunoassay to test 98 CSF samples classified as pyogenic (15), viral (15), self-resolving aseptic meningitis (20), other infectious meningitis (9), neoplastic (4) and normal CSF from patients with (20) and without (15) non-infectious neurological diseases. CSF IL-6 concentrations were increased in pyogenic meningitis (100%) and in more than 50% of viral and other subarachnoid space infections, and rarely in patients without central nervous system infections. Though patients affected by pyogenic meningitis showed the highest levels of CSF IL-6, only a cut-off point greater than or equal to 10000 pg/mL was able to discriminate pyogenic meningitis from those of other aetiologies with a specificity greater than or equal to 94% and a positive predictive value of greater than or equal to 0.75 but the sensitivity was less than or equal to 60%. Therefore, CSF IL-6 concentration is not a good diagnostic marker in the differential diagnosis of meningitis.