Which of the following is not commonly used as a CSF biomarker for multiple sclerosis?

• A. Myelin basic protein
• B. Immunoglobulin G index
• C. Oligoclonal bands
• D. Allantoin

Answer: (D)

In multiple sclerosis, CSF biomarkers reflect immune activity within the central nervous system and active demyelination. Oligoclonal bands are the classic feature: unique IgG patterns in CSF that are not present in serum, indicating intrathecal IgG synthesis. The IgG index provides a quantified measure of that intrathecal IgG production by comparing CSF and serum IgG levels, helping to support CNS-directed immune activity. Myelin basic protein can be elevated when there is active myelin breakdown, offering a signal of ongoing demyelination, especially during relapses, though it’s not as specific as oligoclonal bands.

Allantoin, on the other hand, is not a standard CSF biomarker used in MS. It’s an oxidative stress marker more commonly discussed in other contexts and does not have established diagnostic or monitoring value in the CSF for MS.