Use of amplified Mycobacterium tuberculosis direct test (Gen-probe Inc., San Diego, CA, USA) in the diagnosis of tubercular synovitis and early arthritis of knee joint

BACKGROUND: The diagnosis of knee joint tuberculosis, especially in early stages of synovial disease, has more often been based on clinicoradiological suspicion, with no single test claiming to be a dependable rapid diagnostic test with high sensitivity and specificity. Nuclear amplification tests in vogue like the polymerase chain reaction have shown variable sensitivity and false positivity rates in various studies. We evaluated the role of Amplified Mycobacterium tuberculosis Direct Test (AMTDT) or Genprobe in the diagnosis of knee joint tuberculosis in early, especially, early synovitis and arthritis cases. PATIENTS AND METHODS: Thirty two patients of suspected knee joint tuberculosis were subjected to diagnostic arthroscopy during the study period. The synovial fluid and tissue were subjected to mycobacterial culture, histopathology, and AMTDT. A comparative analysis of the sensitivity and specificity of this new test with culture and histopathology was done and the time taken for reporting was calculated for each test. RESULTS: Out of 32 tissue samples, 8 were found to be positive with mycobacterial culture [Lowenstein Jensen (LJ)/Bactec], 11 were positive with histopathology, and 5 were found to positive with AMTDT. The sensitivity of AMTDT was found to be 62.5% and specificity was 100% with a P value of 0.083. The results were obtained earliest with AMTDT with a mean reporting time of 1.2 days, while the results of histopathology were obtained in a mean time of 6.8 days, BacT alert in 22.5 days, and conventional LJ medium culture results in 48.6 days. CONCLUSION: AMTDT or Genprobe is a rapid diagnostic test for early diagnosis of tubercular arthritis, but has low sensitivity in knee joint tuberculosis. Nuclear amplification tests are still far from being a single promising alternative to conventional tests in cases of joint tuberculosis. Routine use of arthroscopic biopsies in all suspected cases is helpful in the early diagnosis of knee joint tuberculosis.