Multiple sclerosis: problems in the evaluation of intrathecal IgG synthesis.

We report two patients with multiple sclerosis which illustrate problems in the interpretation of the cerebrospinal fluid (CSF) protein studies used to confirm diagnosis. In one case a polyclonal increase in IgG synthesis, secondary to an aseptic meningitis, masked oligoclonal banding, which was confirmed on subsequent examination. In the second case, despite a normal quantitative intrathecal IgG synthesis rate, oligoclonal banding in the CSF confirmed abnormal intrathecal synthesis of IgG. These cases show the value of combining a quantitative index of intrathecal IgG synthesis with examination for oligoclonal banding and illustrate their interpretation.