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Specificity and diagnostic utility of CSF CXCL13 in Lyme neuroborreliosis.

BACKGROUND
Demonstration of intrathecal production of Borrelia-specific antibodies (ITAb) is considered the most specific diagnostic marker of Lyme neuroborreliosis (LNB). Limitations include delayed detectabilty in early infection and continued presence long after successful treatment. Markers of active inflammation - increased CSF leukocytes, protein and CXCL13 - provide nonspecific markers of active infection. To assess the utility of CSF CXCL13, we measured its concentration in 132 patients with a broad spectrum of neuroinflammatory disorders, including LNB.


METHODS
CSF CXCL13 was measured by immunoassay. Spearman's rank correlation test was performed to explore its relationship to conventional markers of neuroinflammation and Borrelia-specific ITAb production.


RESULTS
In non-LNB neuroinflammatory disorders, CSF CXCL13 elevation correlated with CSF IgG synthesis and leukocyte count. In LNB, CXCL13 concentration was far greater than expected from overall CSF IgG synthesis, and correlated with Borrelia-specific ITAb synthesis. Median CSF CXCL13 concentration in ITAb-positive LNB patients was >500 times greater than in any other group.


CONCLUSIONS
Intrathecal CXCL13 and IgG production are closely inter-related. CXCL13 is disproportionately increased in "definite LNB," defined as having demonstrable Borrelia-specific ITAb, but not "probable LNB," without ITAb. This disproportionate increase may help identify patients with very early infection, those with active vs. treated LNB, or help differentiate ITAb-defined active LNB from other neuroinflammatory disorders. However, its reported specificity is closely related to the diagnostic requirement for ITAb. It may add little specificity to the demonstration of a pleocytosis or increased overall or specific IgG production in the CSF.