Kappa index, or K-index, can be a useful tool for diagnosing multiple sclerosis (MS) and predicting the risk of evolution to MS in patients with clinically isolated syndrome (CIS), according to a new study published in Clinical Immunology.

The researchers determined several cut-off values for the K-index to achieve optimal sensitivity and specificity as compared with the current standard prognostic indicator, immunoglobulin G oligoclonal bands (OCB).

“OCB determination remains limited to specialized laboratories since this manual or semi-automated technique requires visual reading by experts,” the authors explained. “To circumvent limitations of OCB determination, alternatives have been developed and among them the kappa (K)-index has emerged as a valuable tool in MS diagnosis.”


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The research team conducted a retrospective analysis of K-index performance compared to OCB determinations in 274 consecutive patients at a single center between April and December 2021. Forty-eight patients had MS and 29 had CIS. The remaining patients had other inflammatory central nervous system diseases, neurotropic infections, or peripheral neurological diseases.

The results showed that the K-index was useful as a new diagnostic tool for MS, particularly when scaled to 3 cut-off points. A K-index of <3.3 had an increased negative predictive value, meaning MS was unlikely in these patients and therefore OCB determination might not be necessary.

A K-index of 9.1 achieved a diagnostic specificity and sensitivity similar to that of OCB, and a very high K-index of >55 was specific to MS. The authors recommend integrating the K-index into the diagnostic criteria for MS, for which a consensus recommendation from MS experts will be needed.

Reference

Marlas M, Bost C, Dorcet G, et al. Kappa-index: real-life evaluation of a new tool for multiple sclerosis diagnosis. Clin Immunol. Published online June 12, 2022. doi:10.1016/j.clim.2022.109066