Meningeal carcinomatosis: origin of local IgG production in the CSF.

We found that eight of 22 patients with meningeal carcinomatosis from different primary tumors produced local IgG in the CSF, as indicated by elevated IgG index and/or oligoclonal IgG subfractions. Local IgG production, when present, appears in an early stage of the leptomeningeal manifestation and remains detectable over extended observation periods. In autopsied cases with local IgG production, we observed numerous perivascular round-cell infiltrates containing plasma cells and large lymphocytes within the leptomeningeal tumor tissue. After incubation with immunoperoxidase, only these cells showed IgG-specific staining, indicating the site of local IgG production.