Intrathecal synthesis of IgG in benign intracranial hypertension: a re-examination.

In a previous retrospective study, 4 of 9 patients with benign intracranial hypertension were unexpectedly positive for intrathecal synthesis of immunoglobulin (Ig) G by quantitative measurement (log IgG index). This was remarkable as the only disease among many studied that showed such a discrepancy. A further study was done, now prospectively. Log IgG index values were elevated in 2 of the 11 new cases. As before, qualitative measurement (isoelectric focusing) gave uniformly negative results. Five of the 6 instances where the log IgG index was elevated could be accounted for, in fact, by abnormal values of constituent variables other than cerebrospinal fluid IgG. Quantitative tests for intrathecal synthesis of IgG can give misleading results on their own. Immunological mechanisms most probably are not involved in the pathogenesis of benign intracranial hypertension.