Cerebrospinal fluid oligoclonal IgM in multiple sclerosis: analytical problems and clinical limitations

Area of Science:

• Neuroimmunology
• Biochemical diagnostics

Background:

• Oligoclonal bands in cerebrospinal fluid (CSF) are key biomarkers for neurological diseases, particularly multiple sclerosis (MS).
• While oligoclonal immunoglobulin G (IgG) is routinely assessed, the diagnostic role of oligoclonal immunoglobulin M (IgM) remains less defined.

Purpose of the Study:

• To describe and validate a novel method for detecting oligoclonal IgM in CSF.
• To evaluate the diagnostic utility of CSF oligoclonal IgM in comparison to oligoclonal IgG, especially for multiple sclerosis (MS).

Main Methods:

• Development of a sensitive assay using agarose isoelectric focusing, poly(vinyl difluoride) blotting, and double-antibody immunoperoxidase staining with avidin-biotin amplification for CSF IgM.
• Implementation of specific conditions to prevent cross-reactivity with IgG.
• Application of the method to 99 patients, including those with and without MS, and comparison with existing oligoclonal IgG analysis.

Main Results:

• The assay successfully detected oligoclonal IgM in CSF.
• Positive oligoclonal IgM results were found in 17/27 patients with oligoclonal IgG and in 2/72 patients without oligoclonal IgG.
• Oligoclonal IgM was not detected in MS patients lacking oligoclonal IgG, but was present in some non-MS patients with oligoclonal IgG.
• CSF oligoclonal IgM demonstrated lower sensitivity and did not improve specificity compared to CSF oligoclonal IgG for MS diagnosis.

Conclusions:

• The described method reliably detects CSF oligoclonal IgM.
• CSF oligoclonal IgM is less sensitive and specific than oligoclonal IgG for diagnosing multiple sclerosis (MS).
• Oligoclonal IgM may be present in other neurological conditions associated with oligoclonal IgG.