Objective: The detection of oligoclonal immunoglobulin free light chains (FLC) in the diagnosis of multiple sclerosis (MS) was compared to IgG isoelectric focusing.

Methods: Cerebrospinal fluid and serum samples from 69 patients with possible first attacks of MS, 50 patients with clinically definite MS (CDMS), and 118 patients with other neurological diseases (OND) were analyzed. IgG and FLC oligoclonal bands were detected by isoelectric focusing and immunoperoxidase staining.

Results: Intrathecal synthesis of IgG, kappa FLC, and lambda FLC oligoclonal bands, respectively, was seen in 92%, 92%, and 86% of MS patients; in 61%, 62%, and 64% of patients with possible first attacks of MS; and in 3%, 3%, and 8% of the patients with OND. In control patients without IgG synthesis intrathecal lambda FLC synthesis was more common than kappa FLC synthesis (P=0.03).

Conclusions: Kappa FLC detection proved as useful as IgG analysis for the laboratory diagnosis of MS whereas the presence of intrathecal lambda FLC synthesis was less specific.