Performance of cytology, acid-fast bacilli smear, gene Xpert and mycobacterial cultures in endobronchial ultrasound-transbronchial needle aspiration aspirate in diagnosing mediastinal tuberculous lymphadenitis

BACKGROUND: Diagnosis of isolated mediastinal tuberculosis (TB) can be challenging. Endobronchial ultrasound (EBUS) increases the diagnostic yield by direct sonographic visualization of mediastinal and hilar lymph nodes. With the advent of molecular techniques such as Gene Xpert, their addition to the cytology and cultures increases the diagnostic yield and detection of rifampicin resistance (RR) which helps change the effective therapeutic regimen immediately. MATERIALS AND METHODS: Prospective analysis of all patients undergoing EBUS-guided transbronchial needle aspiration (EBUS-TBNA) with a clinical possibility of TB in isolated mediastinal lymphadenopathy patients at a tertiary care referral center between June 2016 and January 2018. All patients had at least five passes from each node of which two passes from each lymph node sampled in 2 ml of saline for culture and Gene Xpert for microbiologic, pathologic, and molecular analysis as per hospital protocol. RESULTS: Out of 60 patients, 44 were diagnosed to have mediastinal tuberculous lymphadenitis, 8 sarcoidosis, 2 malignancies, and 6 reactive lymphadenitis. TBNA cytology was positive in 40/44 patients (90.9%), out of which 18 patients were culture positive with the sensitivity of 100%, specificity 47.6%, positive predictive value (PPV) 45%, and negative predictive value (NPV) 100%, (P value 0.011). TBNA acid-fast bacilli (AFB) smear was positive in 20/44 patients (45.45%) out of which 12 were culture positive, with sensitivity of 67%, specificity 80.95%, PPV 60%, NPV 85% (P value 0.011). TBNA Gene Xpert was positive in 30/44 patients (68.2%), out of which 6 (13.63%) showed RR-TB and two were cytology negative. Sixteen patients where culture positive with sensitivity of 88.89%, specificity 66.67%, PPV 53.33%, NPV 93.33% (P value of 0.005). TBNA AFB culture was positive in 18/44 patients (40.9%). CONCLUSION: EBUS-TBNA is an effective and safe diagnostic tool for intrathoracic TB, especially for mediastinal tuberculous lymphadenitis. The combination of various tests increases the diagnostic yield. Mediastinal nodal aspirates traditionally believed to be paucibacillary can still be captured by Gene Xpert.