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Kappa Index Versus CSF Oligoclonal Bands in Predicting Multiple Sclerosis and Infectious/Inflammatory CNS Disorders
Diana Ferraro1,2, Roberta Bedin2, Patrizia Natali3
1Neurology Unit, Azienda Ospedaliero-Universitaria of Modena, 41126 Modena, Italy.
Insights
The kappa index, a marker of intrathecal immunoglobulin synthesis, shows diagnostic accuracy comparable to CSF oligoclonal IgG bands for Multiple Sclerosis and CNS infectious/inflammatory disorders.
Area of Science:
- Neurology
- Immunology
- Clinical Diagnostics
Background:
- Cerebrospinal fluid (CSF) kappa free light chains (KFLC) are emerging biomarkers for intrathecal immunoglobulin synthesis.
- Assessing KFLC's diagnostic utility is crucial for neurological and inflammatory conditions.
Purpose of the Study:
- To evaluate the diagnostic accuracy of the kappa index compared to CSF oligoclonal IgG bands (OCB).
- To determine the predictive value for Multiple Sclerosis (MS) and central nervous system infectious/inflammatory disorders (CNSID).
Main Methods:
- Analysis of 540 patients undergoing diagnostic spinal taps over two years.
- Quantification of KFLC levels using Freelite assay and Optilite analyzer.
- Comparison of kappa index and OCB performance metrics (sensitivity, specificity, AUC).
Main Results:
- For MS diagnosis, the kappa index demonstrated higher sensitivity (0.89 vs. 0.85) and lower specificity (0.84 vs. 0.89) than OCB, with an identical AUC of 0.87.
- For CNSID diagnosis, the kappa index (AUC 0.74) was more sensitive (0.67 vs. 0.50) but less specific (0.81 vs. 0.97) compared to OCB.
- Adding single CSF IgG bands to OCB slightly improved MS diagnostic AUC to 0.88.
Conclusions:
- The kappa index and CSF OCB exhibit comparable diagnostic accuracies for MS and CNSID.
- Both markers provide valuable and complementary clinical information for diagnosing neurological and inflammatory conditions.
Background:
Cerebrospinal fluid (CSF) kappa free light chains (KFLC) are gaining increasing interest as markers of intrathecal immunoglobulin synthesis. The main aim of this study was to assess the diagnostic accuracy (AUC) of the kappa index (CSF/serum KFLC divided by the CSF/serum albumin ratio) compared to CSF oligoclonal IgG bands (OCB) in predicting Multiple Sclerosis (MS) or a central nervous system infectious/inflammatory disorder (CNSID).
Methods:
We enrolled patients who underwent a diagnostic spinal tap throughout two years. KFLC levels were determined using a Freelite assay (Binding Site) and the turbidimetric Optilite analyzer.
Results:
Of 540 included patients, 223 had a CNSID, and 84 had MS. The kappa index was more sensitive (0.89 versus 0.85) and less specific (0.84 versus 0.89), with the same AUC (0.87) as OCB for MS diagnosis (optimal cut-off: 6.2). Adding patients with a single CSF IgG band to the OCB-positive group slightly increased the AUC (0.88). Likewise, the kappa index (cut-off: 3.9) was more sensitive (0.67 versus 0.50) and less specific (0.81 versus 0.97), with the same AUC (0.74) as OCB, for a CNSID diagnosis.
Conclusion:
The kappa index and CSF OCB have comparable diagnostic accuracies for a MS or CNSID diagnosis and supply the clinician with useful, complementary information.
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