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Updated: Jan 17, 2026
Magnetic Resonance Imaging of Multiple Sclerosis at 7.0 Tesla
Published on: February 19, 2021
Positive cerebrospinal fluid in the 2024 McDonald criteria for multiple sclerosis
Florian Deisenhammer1, Harald Hegen1, Georgina Arrambide2
1Department of Neurology, Innsbruck Medical University, Innsbruck, Austria.
Insights
The 2024 McDonald criteria for Multiple Sclerosis (MS) now include kappa free light chains (κ-FLC) as an alternative to oligoclonal IgG bands (OCB) for diagnosing MS. κ-FLC offers comparable diagnostic accuracy and potential prognostic value.
Area of Science:
- Neurology
- Immunology
- Clinical Diagnostics
Background:
- The 2024 McDonald diagnostic criteria for Multiple Sclerosis (MS) have been updated.
- Intrathecal immunoglobulin synthesis is a key diagnostic marker for MS.
Purpose of the Study:
- To evaluate the role of kappa free light chains (κ-FLC) in cerebrospinal fluid (CSF) as a diagnostic marker for MS.
- To compare the diagnostic performance of κ-FLC with oligoclonal IgG bands (OCB).
- To assess the prognostic utility of κ-FLC and Neurofilament light (NfL) in MS.
Main Methods:
- Analysis of diagnostic sensitivity and specificity of κ-FLC detection in CSF.
- Comparison of κ-FLC results with OCB findings.
- Calculation and evaluation of the κ-FLC index for MS diagnosis.
- Review of available assays and proficiency testing for κ-FLC measurement.
Main Results:
- κ-FLC detection in CSF demonstrates diagnostic sensitivity and specificity equal to OCB for MS.
- A κ-FLC index value of ≥6.1 is recommended for optimal MS diagnosis.
- Concordance between κ-FLC and OCB is approximately 90%, with combined testing useful in rare cases.
- Higher κ-FLC index values may predict increased MS disease activity, suggesting prognostic value.
- Neurofilament light (NfL) is not recommended for MS diagnosis but may aid prognosis and monitoring.
Conclusions:
- κ-FLC detection in CSF is a reliable and interchangeable alternative to OCB for diagnosing MS according to the 2024 McDonald criteria.
- Validated assays and proficiency testing are crucial for accurate κ-FLC measurement.
- The κ-FLC index holds potential for both diagnosis and prognosis in pediatric and adult MS patients across various disease courses.
Abstract:
The 2024 McDonald diagnostic criteria for Multiple Sclerosis (MS) introduce kappa free light chains (κ-FLC) detection in cerebrospinal fluid (CSF) which can be used interchangeably with oligoclonal IgG bands (OCB) to demonstrate intrathecal immunoglobulin synthesis. Diagnostic sensitivity and specificity of κ-FLC is equal to OCB on a 95% confidence level. In rare cases determination of both, κ-FLC and OCB should be considered as the concordance rate is around 90%. We recommend calculating the κ-FLC index with values of ≥6.1 performing best for diagnosing MS. Validated turbidimetric or nephelometric assays should be applied for which proficiency testing programs are available. There is some prognostic use of the κ-FLC index with higher values predicting higher disease activity. Neurofilament light (NfL) should not be used for diagnostic purposes although it might be useful for prognosis and disease monitoring. All recommendations apply to paediatric and adult relapsing as well as progressive onset MS.
