To assess, in a single centre study the sensitivity and specificity of kappa free light chain index for the diagnosis of MS.

It has been shown that kappa free light chain assessment and kappa free light chain index could be an additional diagnostic biomarker of interest in the setting of multiple sclerosis.

We performed a retrospective analysis of 25 primary progressive MS patients and 17 patients with other inflammatory neurological disorders who had been previously CSF sampled and who had available CSF oligoclonal bands result. kappa free light chain assessment and kappa free light chain index were measured. Sensitivity and specificity were defined according to the recently proposed cut-off of 6.6.

In MS patients, mean CSF kappa free light chain values were 9.03+/-7.7 mg/L and mean index was 88 +/-100.3. In other inflammatory neurological disorders, mean CSF kappa light chains values were under the detection threshold in 13 patients and mean values were 3.82mg/L +/-3.5 in the remaining patients. Kappa free light chain index was not quantifiable in 13 patients and was equal to 46.3+/-47.5 in the 4 remaining patients. At the cut-off of kappa free light chain index of 6.6, sensitivity and specificity for the diagnosis of multiple sclerosis were respectively 96% and 82.4%. Meanwhile, oligoclonal bands had lower sensitivity (86%) but higher specificity (94%).

Our data are in line with previous studies suggesting that kappa free light chain assessment has higher sensitivity for the diagnosis of MS but at the price of reduced specificity. An analysis on a larger sample of MS patients and controls is ongoing and will be presented at the meeting.