Diagnostic criteria for Tuberculous Meningitis

Objective : Tuberculous Meningitis is associated with a high morbidity and mortality if there is a delay in diagnosis. The diagnosis is based on clinical evaluation since the bacteriological diagnosis takes time and has a low yield. This study attempts to validate these criteria in children with TBM. Methods : Forty-two children clinically suspected to have TBM were enrolled in the study. History, examination, CT scan and CSF findings were utilized to categorize patients into "definite", "highly probable", "probable" and "possible" TBM based on the criteria laid down by Ahuja et al. The validity of these criteria was tested against bacterial isolation and response to treatment. Results : Thirty one children, with complete data, were included for analysis. Using "improvement on therapy" as a criterion for definite TBM, we analyzed the sensitivity and specificity of the Ahuja criteria in diagnosing TBM. Using the criteria of "highly probable" TBM, the sensitivity was 65% with a specificity of 75%. When the criteria of "probable" TBM were used, the sensitivity increased to 96% while the specificity dropped to 38%. In an attempt to make these criteria more appropriate for children, we modified the criteria by including mantoux reaction, and family history of exposure in the criteria. The modified criteria gave a sensitivity of 83% and a specificity of 63%. Discussion : A sensitivity of 65% (highly probable group) implies that 35% of TBM patients will be missed, while the probable criteria gave a 63% false positive rate suggesting that the trade-off for a higher sensitivity makes the criteria very unreliable. Our modification of the criteria gave us a reasonable sensitivity of 83% with a higher specificity of 63%. The false positive rate was also reduced to 38%. Thus the modified Ahuja criteria worked better for children with TBM. Conclusion : The modified Ahuja criteria are better applicable for use in pediatric patients with TBM . Since the number of patients was small in this study, the study needs to be validated with a larger sample size.