CSF interleukin 6 is a useful marker to distinguish pseudotumoral CNS inflammatory diseases from primary CNS lymphoma

BACKGROUND Interleukin 6 (IL-6) is a pleomorphic cytokine that can be found in the cerebrospinal fluid (CSF) in a wide spectrum of inflammatory pathologies of the central nervous system (CNS). OBJECTIVE Our aim was to characterize the diagnostic significance of CSF IL-6 among various CNS inflammatory diseases with pseudotumoral lesions (CNSID) and primary CNS lymphoma (PCNSL). METHODS We retrospectively analyzed the CSF IL-6 concentrations in 43 consecutive patients with suspected PCNSL. A total of 28 patients were positively diagnosed with PCNSL and 15 with CNSID. We verified the results with CSF IL-10, an established biomarker for PCNSL. RESULTS In the PCNSL group, the median CSF IL-6 concentration was 8 pg/ml, interquartile range (IQR) 5-18.5. For the patients with CNSID, the median concentration was 70 pg/ml, IQR 5-1368. A group comparison showed significantly higher CSF IL-6 levels in patients with CNSID than in those with PCNSL (p = 0.032). Moreover, IL-6 was correlated with CSF cell count in the CNSID group (r = 0.56, p = 0.028), but not in the PCNSL group (r = 0.3, p = 0.13). We found significantly higher CSF IL-10 levels in patients with PCNSL than in patients with CNS inflammatory lesions (p < 0.001). DISCUSSION AND CONCLUSIONS Our study suggests that CSF IL-6 levels could represent, in addition to CSF IL-10, a useful biomarker in the differential diagnosis of CNSID and suspected PCNSL.