Cerebrospinal fluid free light chains as diagnostic biomarker in neuroborreliosis

BACKGROUND: Free light chains (FLC) have been proposed as diagnostic biomarker in patients with inflammatory central nervous system diseases. The objective of this study was to investigate the diagnostic utility of intrathecal κ- and λ-FLC synthesis in patients with neuroborreliosis. METHODS: κ- and λ-FLC were measured by nephelometry under blinded conditions in cerebrospinal fluid (CSF) and serum sample pairs of 34 patients with neuroborreliosis and compared to a cohort of 420 control patients. κ-FLC index was calculated as [CSF κ-FLC/serum κ-FLC]/[CSF albumin/serum albumin], and λ-FLC index in analogy. RESULTS: κ-FLC and λ-FLC index were significantly elevated in patients with neuroborreliosis compared to the control group. At a specificity level of 95%, κ-FLC and λ-FLC index showed a diagnostic sensitivity of 88.2% and 100%. In comparison, IgM and IgG synthesis according to Reiber formula, IgG index >0.7 and OCB status reached a sensitivity of 83.9%, 44.1%, 58.8% and 64.7%. CONCLUSION: These findings support the diagnostic value of intrathecal FLC synthesis in neuroborreliosis patients and demonstrate a valid, easy and rater-independent alternative for the detection of an intrathecal immunoglobulin production.