Collection of cerebrospinal fluid kappa and lambda free light chains and indexes

1. Measurement of cerebrospinal fluid (CSF) and serum KFLC and LFLC by a turbilimetric analyzer (data in mg/L)
2. Quantification of QKFLC and QLFLC (CSF FLC/serum FLC) in each group of patients
3. Compare median of QKFLC and QLFLC between groups

1. Measurement of cerebrospinal fluid (CSF) and serum albumin by the same turbilimetric analyzer (data in mg/L)
2. Quantification of albumin quotient (AQ) (CSF albumin/serum albumin) in each group of patients

1. Calculation of KFLC intrathecal synthesis biomarkers:

   KFLC index = (CSF KFLC/serum KFLC) / AQ

   KFLC IF = (KFLC(loc)/CSF KFLC) x 100 with:

   KFLC(loc) = ((CSF KFLC/serum KFLC) / Qk(lim)) x serum KFLC and Qk(lim) = 3.27 x (AQ^2 + 33)^0.5 - 8.2

2. Calculation of LFLC intrathecal synthesis biomarkers:

   LFLC index = (CSF LFLC/serum LFLC) / AQ)

   LFLC IF = (LFLC(loc)/CSF LFLC) x 100 with:

   LFLC(loc) = ((CSF LFLC/serum LFLC) / Ql(lim)) x serum LFLC and Ql(lim) = 2.1138 x AQ^0.865

3. Determination of diagnostic performances by ROC curve analysis and best cut-off values with the Younden index to calculate sensitivity, specificity and predictive values for MS diagnosis

1. Identification of OCB status for each patient
2. Calculation of diagnostic performances of OCB (sensitivity, specificity and predictive values) for MS diagnostic
3. Comparison of diagnostic performances (sensitivity, specificity and predictive values) of OCB and K/L FLC intrathecal synthesis biomarkers for multiple sclerosis

Identification of data that can be independtly associated with high or low CSF KFLC or LFLC values as potential bias in K/L FLC intrathecal synthesis biomarkers interpretation:

• Gender
• Age
• Type of clinical demyelinating event (i.e. myelitis, optic neuritis...)
• Immune modifying drug treatment ongoing during sampling
• Underlying disease activity (measured by the presence of subacute clinical symptoms ongoing at sampling or gadolinium enhanced lesions within the last MRI status)