Pathology of rheumatoid meningitis: A report of 5 cases highlighting the importance of clinical correlation.

Rheumatoid meningitis (RM) presents with sufficiently wide-ranging, but non-specific, symptoms and neuroimaging features of pachy- and/or leptomeningeal thickening that it may be indistinguishable from subacute infectious meningitis. RA diagnosis variably antedates RM and serological confirmation by rheumatoid factor and anti-citrullinated peptide antibodies may not be present preoperatively. Thus, meningeal biopsy may be undertaken. Classic examples of RM show lymphoplasmacytic leptomeningeal inflammation and small vessel vasculitis, with rheumatoid nodules being less frequent. We reviewed our experience with 5 RM biopsies, as well as the literature, placing "classic" histological findings in perspective with biopsies showing less pathognomonic features. 5 RM cases were identified, 2 male: 3 female, ages 62-79 years. All patients had leptomeningeal enhancement by MRI and 2 had known negative RF serology prior to meningeal biopsy. In 1 case RF was initially negative, but on serological reassessment turned positive; 2 patients were diagnosed by clinical correlation. 4 leptomeningeal/superficial cortical biopsies manifested chronic lymphoplasmacytic inflammation with multinucleated giant cells, with discrete foci of deep blue/black necrosis with cellular debris ("dirty necrosis") surrounded by a variably- developed palisade of histiocytes (rheumatoid nodules). The 5th showed only non-specific mononuclear cell inflammation. All showed variable degrees of diffuse astrocytosis and microgliosis of the cortex without microglial clusters or compact granulomas. Stains for microorganisms were negative. Diagnosis of RM can be suspected by the pathologist if the "classic" features of rheumatoid nodules are present on biopsy, but in some cases, only non-specific inflammation is present. Diagnosis necessitates correlation between clinical, serological, and histological features.