Reference values for CSF-IgM, CSF-IgM/S-IgM ratio and IgM index, and its application to patients with multiple sclerosis and aseptic meningoencephalitis.

Immunoglobulin M (IgM) concentrations were determined in cerebrospinal fluid (CSF) and serum (S) by enzyme-linked immunosorbent assay (ELISA). In 52 reference subjects, the upper reference limit was 0.46 mg/l for CSF-IgM, 0.32 X 10(-3) for CSF-IgM/S-IgM ratio, and 0.061 for IgM index equal to CSF-IgM X S-albumin/S-IgM X CSF-albumin ratio. No correlation to age over 15-85 years was found for any of these variables. Among 22 patients with aseptic meningoencephalitis (AM) elevated values of CSF-IgM were found in 68%, CSF-IgM/S-IgM ratio in 73%, and IgM index in 73%. The corresponding values among 35 patients with multiple sclerosis (MS) were 66%, 60% and 63%. The differences in diagnostic sensitivities for the three IgM variables were not significant. Eleven of 16 AM patients and two of 22 with MS had elevated IgM index in the presence of normal IgG and IgA indices. Determination of IgM index should therefore be performed in suspected inflammatory nervous system disorders.