Free Kappa Light Chains in Neuroinflammatory Disorders: Complement Rather Than Substitute?

Acta Neurol Scand. 2018 Oct;138(4):352-358. doi: 10.1111/ane.12969. Epub 2018 Jun 13.

Abstract

Objectives: The detection of cerebrospinal fluid (CSF)-specific IgG oligoclonal bands (OCB) by isoelectric focusing (IEF) is widely used to help diagnose inflammatory neurological disorders (IND), including multiple sclerosis. However, the quantification of free light chains (FLC) is increasingly evaluated as a surrogate method to determine the presence of an intrathecal inflammatory process. The objective of this study was to evaluate the diagnostic performance of kappa (κ) FLC measurement in comparison with OCB detection by IEF.

Material and methods: We measured serum and CSF κFLCs by turbidimetry using the SPAplus automated analyser and calculated the κ index in 142 samples from OCB-positive and negative MS, as well as from patients with inflammatory and non-inflammatory neurological disorders (IND and NIND).

Results: The κFLC index was significantly increased in OCB-positive MS and IND patients versus OCB-negative patients. Its performance was relatively comparable to that of IEF for MS diagnosis. When using a κFLC index cutoff value of 6.29, sensitivity increased from 61.2% to 75.7% in comparison with IEF for diagnosing IND (P = .0051), with a slightly lower non-statistically significant specificity (82.1% vs 100%). When considering both OCB status positivity or a κFLC index superior to 6.29 to diagnose IND status, sensitivity raised to 80.6% (P < .05) with an equal specificity.

Conclusion: Our results demonstrate that the κFLC index does not discriminate MS from other IND patients, but is a reliable technique to detect intrathecal inflammation. However, κFLC quantification should probably be considered as a complementary method, rather than a substitute, to OCB detection.

Keywords: cerebrospinal fluid; free kappa light chains; multiple sclerosis; neuroinflammatory disorders; oligoclonal bands.

MeSH terms

  • Adult
  • Biomarkers / blood
  • Biomarkers / cerebrospinal fluid
  • Female
  • Humans
  • Immunoglobulin G / blood
  • Immunoglobulin G / cerebrospinal fluid
  • Immunoglobulin Light Chains / blood
  • Immunoglobulin Light Chains / cerebrospinal fluid
  • Immunoglobulin kappa-Chains / blood*
  • Immunoglobulin kappa-Chains / cerebrospinal fluid*
  • Inflammation / blood
  • Inflammation / cerebrospinal fluid
  • Inflammation / diagnosis
  • Male
  • Middle Aged
  • Multiple Sclerosis / blood
  • Multiple Sclerosis / cerebrospinal fluid
  • Multiple Sclerosis / diagnosis
  • Nephelometry and Turbidimetry / methods
  • Nervous System Diseases / blood*
  • Nervous System Diseases / cerebrospinal fluid*
  • Nervous System Diseases / diagnosis
  • Oligoclonal Bands / blood
  • Oligoclonal Bands / cerebrospinal fluid
  • Retrospective Studies

Substances

  • Biomarkers
  • Immunoglobulin G
  • Immunoglobulin Light Chains
  • Immunoglobulin kappa-Chains
  • Oligoclonal Bands