Diagnostic scoring system for tuberculous meningitis among adult patients with non-suppurative and non-bacterial meningitis

Tuberculous meningitis (TBM) is the most severe form of extra-pulmonary tuberculosis. The definite diagnosis of this disease is difficult and can result in delayed treatment. Conventional culture yields low sensitivity while high-sensitivity diagnostic techniques are costly and unpractical. Adenosine deaminase (ADA) is used to diagnose several settings of extra-pulmonary tuberculosis but it is limited in TBM especially among HIV-infected patients. We retrospectively reviewed the data of patients with non-suppurative meningitis and compared the patient data with TBM and other causes including carcinomatous, lymphomatous, lymphocytic and fungal meningitis. We found that HIV infection, diabetes mellitus, duration of symptoms <14 days, radiologic findings of hydrocephalus, and CSF ADA level >10 IU were associated with TBM. The scoring system based on these parameters and their coefficients in the final model achieved an area under the receiver operating characteristic curve of 0.95,625. The indices were HIV infection = 5, diabetes mellitus = 3, duration of symptoms <14 days = 5, hydrocephalus = 4, and ADA in CSF >10 IU = 5. Based on the assumed costs of the patients with false negative and false positive, an appropriate cut off value of 10 was selected and the sensitivity was 92% and specificity was 89%.