71 year-old African-American female, retired EMS paramedic, with hypertension, history of ischemic stroke, Hepatitis C, colon cancer s/p resection several years ago was hospitalized for fever, chills and altered mental status. Treatment was started empirically for bacterial meningitis. HIV antibody testing was negative. Subsequently, CSF analysis showed WBC 155 with 90% lymphocytosis, glucose 23, protein 299, but negative for gram stain, AFB smear, bacterial and fungal cultures, and herpes PCR. A further history per family revealed that patient had tested positive for PPD skin test few months ago, and it was unclear if she was treated. We tested serum for quantiferon gold test, which returned positive. CSF Adenosine Deaminase Activity (ADA) was measured at 14.2 U/L/min. Patient was then treated with anti tubercular regimen with clinical improvement.
Our patient was treated for TB meningitis with clinical improvement based on the following results: (+) PPD, (+) serum quantiferon, and ADA 14.2 U/L/min. In our search of literature, we found that determination of ADA activity in CSF of TBM patients using cut off value of 11.39 U/L/min can be useful for early differential diagnosis of TBM sensitivities of 78-96%.5 Also, at this cut off value the sensitivity of ADA test to differentiate between TBM and non-infectious meningitis was 82% and specificity was 83%. Even in a low endemicity area, the best ADA cutoff was 11.5 IU/L with 91 % sensitivity and 77.7 % specificity.
TBM remains a global health problem with resurgence in the developed world as an opportunistic infection. Definitive diagnosis remains difficult due to pleomorphic clinical presentations and variable sensitivities of diagnostic studies. The gold standard remains by either AFB stain on smear and/or culture. However, direct smear methods are often negative and culture can take up to 4-6 weeks, resulting in delayed treatment; therefore, we propose adenosine deaminase as an adjunct laboratory test to diagnosing tuberculosis meningitis.