BACKGROUND:Diagnosis of tuberculous meningitis (TBM) is difficult. Rapid confirmatory diagnosis is essential to initiate required therapy. There are very few published reports about the diagnostic significance of 65 kD heat shock protein (hsp) in TBM patients, which is present in a wide range of Mycobacterium tuberculosis species and elicits a cellular and humoral immune response. In the present study we have conducted a prospective evaluation for the demonstration of 65 kD hsp antigen in cerebrospinal fluid (CSF) of TBM patients, by indirect ELISA method using monoclonal antibodies (mAb) against the 65 kD hsp antigen, for the diagnosis of TBM. METHODS:A total of 160 CSF samples of different groups of patients (confirmed TBM {n = 18}, clinically suspected TBM {n = 62}, non TBM infectious meningitis {n = 35} and non-infectious neurological diseases {n = 45}) were analyzed by indirect ELISA method using mAb to 65 kD hsp antigen. The Kruskal Wallis test (Non-Parametric ANOVA) with the Dunnett post test was used for statistical analysis. RESULTS:The indirect ELISA method yielded 84% sensitivity and 90% specificity for the diagnosis of TBM using mAb to 65 kD hsp antigen. The mean absorbance value of 65 kD hsp antigen in TBM patients was [0.70 +/- 0.23 (0.23-1.29)], significantly higher than the non-TBM infectious meningitis group [0.32 +/- 0.14 (0.12-0.78), P < 0.001] and also higher than the non-infectious neurological disorders group [0.32 +/- 0.13 (0.20-0.78), P < 0.001]. A significant difference in the mean absorbance of 65 kD hsp antigen was noted in the CSF of culture-positive TBM patients [0.94 +/- 0.18 (0.54-1.29)] when compared with clinically suspected TBM patients [0.64 +/- 0.20 (0.23-0.98), P < 0.05]. CONCLUSION:The presence of 65 kD hsp antigen in the CSF of confirmed and suspected cases of TBM would indicate that the selected protein is specific to M. tuberculosis and could be considered as a diagnostic marker for TBM.