A nontuberculous, lymphocytic meningitis with a low C.S.F. sugar level may be confused with a tuberculous meningitis. Additional diagnostic help may be obtained from examination of the blood. The blood pictures of twelve patients with tuberculous meningitis were compared with those from ten patients with a nontuberculous, nonbacterial lymphocytic meningitis, four of whom had low C.S.F. sugar levels. These ten patients appeared clinically to be suffering from the same disease and only the serum complement fixation test for lymphocytic choriomeningitis showed them to be a heterogeneous group.

The main differences in the blood were (1) a uniformly low total white cell count in the benign meningitis group as opposed to a widely varying total white cell count in tuberculous meningitis; (2) a lower percentage count of polymorphs in the benign lymphocytic meningitis group; (3) the presence of atypical plasma cells in nine of the ten patients in the benign, lymphocytic meningitis group. Two of the patients with benign meningitis, who had repeatedly given negative Paul-Bunnell tests showed a blood picture indistinguishable from that of glandular fever.

Although these atypical plasma cells are not specific for lymphocytic choriomeningitis or for virus diseases in general, they were found in no case of tuberculous meningitis. The presence of these cells is therefore of considerable aid in excluding a diagnosis of tuberculous meningitis.

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