Diagnostic performance of cerebrospinal fluid free light chains in Lyme neuroborreliosis - a pilot study.

Background: The aim of this study was to evaluate the diagnostic performance of cerebrospinal fluid (CSF) free light chains (FLCs) in the diagnosis of Lyme neuroborreliosis (LNB). Methods: Serum and CSF levels of kappa- and lambda-FLC, albumin and total concentration of immunoglobulin M (IgM) were determined together with CSF chemokine CXCL13 in 23 patients with definite LNB, 35 inflammatory neurological disease control (INDC) and 18 non-inflammatory control (NIC) patients. Indices and intrathecal fractions (IFs) of FLC and IgM were calculated. Results: Significant differences in FLC indices and IFs were found between the LNB group and both control groups, p <= 0.007. Sensitivity of intrathecal kappa- and lambda-FLC synthesis reached 78%-87% in LNB patients with a specificity of 94%-100% in NIC patients, whereas specificity in INDC patients was 69%. The corresponding frequencies of positive results for IF and index of IgM and CSF CXCL13 in these three diagnostic groups were 74%-96% in LNB patients, 0% in NIC patients and 3%-6% in INDC patients at the chosen cut-off levels. Conclusions: The findings of this study show a moderate to high sensitivity of CSF kappa- and lambda-FLC in LNB patients with a high specificity in NIC patients. However, overlap in CSF kappa- and lambda-FLC levels between LNB and INDC patients calls for caution in the interpretation and limits the diagnostic usefulness in the LNB diagnosis. CSF CXCL13 appears to be the most valuable additional biomarker of LNB aside from routine parameters such as CSF pleocytosis and antiBorrelia antibody index.