High sensitivity and specificity of elevated cerebrospinal fluid kappa free light chains in suspected multiple sclerosis

• CSF κ free light chains in multiple sclerosis are sensitively measured by nephelometry
• CSF κ free light chains were highly specific for multiple sclerosis
• Analysis of CSF κ free light chain concentration alone is a sufficient measurement

Cerebrospinal fluid (CSF) analysis is routinely used in the diagnostic work-up of multiple sclerosis (MS), by detecting CSF-specific oligoclonal bands (OCB). More recently, several studies have reported CSF free light chains (FLC) as an alternative. We show that absolute CSF κFLC concentrations were highly sensitive — more than OCB testing — and specific for clinically isolated syndrome, relapsing remitting and primary progressive MS. Measurement of κFLC alone was sufficient. Our results suggest that CSF κFLC levels measured by nephelometry, if validated in a larger series, are a preferred test to OCB analysis in the diagnostic work-up of patients suspected of having MS.