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Kappa Free Light Chain Biomarkers Are Efficient for the Diagnosis of Multiple Sclerosis: A Large Multicenter Cohort
Michael Levraut1, Sabine Laurent-Chabalier2, Xavier Ayrignac2
1From the Unité de Recherche Clinique Cote d'Azur-UR2CA URRIS (M.L., C.L.-F.), Centre Hospitalier Universitaire de Nice; Département de Biostatistiques (S.L.-C.), Epidémiologie clinique et Santé Publique, Centre Hospitalier Universitaire de Nîmes; Département de Neurologie (X.A., P.L.), Centre Hospitalier Universitaire de Montpellier, Montpellier; Département de Neurologie (K.B., J.D.S.), Centre Hospitalier Universitaire de Strasbourg; Service de Neurologie (M.R., E.T.), Centre Hospitalier Universitaire de Nîmes; Laboratoire de Biochimie (S.S.), Centre Hospitalier Universitaire de Nîmes; Département de Neurologie (H.Z., T.A.), Centre Hospitalier Universitaire de Lille; Centre Hospitalier Universitaire de Lille (J.-D.P.), Service de Biochimie Automatisée, Protéines (UF 8833), Lille; Département de Neurologie (J.C., D.B.), Centre Hospitalier Universitaire de Toulouse, Hôpital Pierre-Paul Riquet, CRC-SEP, F-31059, Toulouse Cedex 9; Laboratoire d'Immunologie (B.P.-L.), Centre Hospitalier Universitaire de Toulouse; Département de Neurologie (J.-P.C.), Centre Hospitalier Universitaire de Saint-Etienne; Laboratoire de Biochimie (Y.T.), Centre Hospitalier Universitaire de Saint-Etienne; Département de Neurologie (O.C.), Centre Hospitalier Universitaire de Grenoble Alpes; Univ. Grenoble Alpes (B.T.), CNRS, UMR 5525, VetAgro Sup, Grenoble INP, CHU Grenoble Alpes, TIMC; Laboratoire de Biochimie (B.T., J.M.), Centre Hospitalier Universitaire de Grenoble Alpes; Département de Neurologie (T.M.), Centre Hospitalier de Dijon; Laboratoire de Biochimie (D.L., A.T.), Centre Hospitalier Universitaire de Dijon; Département de Neurologie (E.M.), Assistance-Publique des Hôpitaux de Paris, Centre Hospitalier Universitaire de la Pitié-Salpêtrière; Laboratoire d'Immunologie (D.S.), Assistance Publique des Hôpitaux de Paris, Centre Hospitalier Universitaire de la Pitié-Salpêtrière, Paris; Département de Neurologie (A.M., A.R.), Centre Hospitalier Universitaire de Tours; Université de Nantes (D.A.L.), C2RTI Inserm UMR1064, service de Neurologie, CHU Nantes; Département de Biochimie (E.B.-C., P.-O.B.), Centre Hospitalier Universitaire de Nantes; Aix Marseille Univ (J.P.), APHM, Hôpital de la Timone, Pôle de Neurosciences Cliniques, Service de Neurologie; Laboratoire de Biochimie (J.B.), Assistance Publique des Hôpitaux de Marseille, Centre Hospitalier Universitaire de La Conception; Laboratoire d'Immunologie (T.V.), Centre Hospitalier Universitaire de Montpellier; Laboratoire d'Immunologie (I.J.), Centre Hospitalier Universitaire Strasbourg; Laboratoire d'Immunologie (B.S.-P.), Centre Hospitalier Universitaire de Nice; Institut de Génomique Fonctionnelle (E.T.), Université de Montpellier, CNRS, INSERM, Montpellier; and Département de Neurologie (C.L.-F.), Centre Hospitalier Universitaire de Nice, France. michael.levraut@gmail.com.
Background And Objectives:
Kappa free light chains (KFLC) seem to efficiently diagnose MS. However, extensive cohort studies are lacking to establish consensus cut-offs, notably to rule out non-MS autoimmune CNS disorders. Our objectives were to (1) determine diagnostic performances of CSF KFLC, KFLC index, and KFLC intrathecal fraction (IF) threshold values that allow us to separate MS from different CNS disorder control populations and compare them with oligoclonal bands' (OCB) performances and (2) to identify independent factors associated with KFLC quantification in MS.
Methods:
We conducted a retrospective multicenter study involving 13 French MS centers. Patients were included if they had a noninfectious and nontumoral CNS disorder, eligible data concerning CSF and serum KFLC, albumin, and OCB. Patients were classified into 4 groups according to their diagnosis: MS, clinically isolated syndrome (CIS), other inflammatory CNS disorders (OIND), and noninflammatory CNS disorder controls (NINDC).
Results:
One thousand six hundred twenty-one patients were analyzed (675 MS, 90 CIS, 297 OIND, and 559 NINDC). KFLC index and KFLC IF had similar performances in diagnosing MS from nonselected controls and OIND (p = 0.123 and p = 0.991 for area under the curve [AUC] comparisons) and performed better than CSF KFLC (p < 0.001 for all AUC comparisons). A KFLC index of 8.92 best separated MS/CIS from the entire nonselected control population, with better performances than OCB (p < 0.001 for AUC comparison). A KFLC index of 11.56 best separated MS from OIND, with similar performances than OCB (p = 0.065). In the multivariate analysis model, female gender (p = 0.003), young age (p = 0.013), and evidence of disease activity (p < 0.001) were independent factors associated with high KFLC index values in patients with MS, whereas MS phenotype, immune-modifying treatment use at sampling, and the FLC analyzer type did not influence KFLC index.
Discussion:
KFLC biomarkers are efficient tools to separate patients with MS from controls, even when compared with other patients with CNS autoimmune disorder. Given these results, we suggest using KFLC index or KFLC IF as a criterion to diagnose MS.
Classification Of Evidence:
This study provides Class III evidence that KFLC index or IF can be used to differentiate patients with MS from nonselected controls and from patients with other autoimmune CNS disorders.
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