A new study has reported that the kappa free light chain index (K-index) can predict the occurrence of new T2 lesions in subjects with clinically isolated syndrome (CIS) and radiologically isolated syndrome (RIS) (Levraut et al. Neurol Neuroimmunol Neuroinflamm 2023;10:e200156). The K-index was also useful to predict clinical events in CIS.

The study obtained blood and CSF from 146 CIS patients and 36 individuals with RIS. Median age for the two groups was 38 and 46 years, respectively. The K-index was calculated as the ratio of kappa free light chain in CSF and serum divided by the ratio of albumin in CSF and serum. A value >8.9 was considered to be positive based on the results of a previous study (Levraut M et al. Neurol Neuroimmunol Neuroinflam 2022;10:e200049).

Median K-index values were 36.9 for CIS and 18.3 for RIS. The proportion that was OCB+ was similar (54% and 44%, respectively). Overall, 82% had both elevated K-index and OCB positivity. In the CIS group, 48% had at least one Gd+ lesion and 53% met 2017 McDonald criteria for MS. In the subgroup that met MS criteria because of OCB positivity, the median K-index was 103.0 (minimum 35.3). K-index values were higher in patients with Gd+ lesions.

During the median 21-month follow-up, 58% had at least one new T2 lesion. The K-index was prognostic of new T2 lesions in CIS (AUC 0.86 at 12 months) and RIS (AUC 0.84 at 12 months). The risk of a new T2 lesion increased 6% with every 10-point increase in the K-index in CIS, and 8% with every 10-point increase in RIS. The K-index was a better predictor of T2 lesions than other measures such as the number of dissemination-in-space locations of T2 lesions at baseline, the presence of Gd+ lesions or OCB status. Notably, OCB positivity was not predictive of new T2 lesions in RIS.

Moreover, the K-index was predictive of a clinical attack in CIS (AUC 0.75 at 12 months). The risk of a relapse in CIS patients increased by 4% with each 10-point increase in the K-index.

The authors concluded that the K-index might be useful biomarker in CIS to demonstrate dissemination in time. The K-index may also be helpful to identify individuals with RIS at risk of ongoing disease activity.