A PUZZLING CASE OF MYCOBACTERIAL LUNG DISEASE

Abstract

SESSION TITLE: Chest Infections 4 SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/09/2018 01:15 PM - 02:15 PM INTRODUCTION: There are over 150 species of mycobacteria that have been described to date. Pulmonary infections are most commonly due to Mycobacteria tuberculosis (MTB), however nontuberculous mycobacteria (NTM) are increasingly recognized worldwide, making microbial identification an important step in early management as drug treatment can vary significantly between species. CASE PRESENTATION: A 49-year-old male from Kenya presented with severe life-threatening hemoptysis, preceded by 4 days of productive cough and dyspnea. An urgent bronchoscopy identified active bleeding in the right upper lobe that was not amendable to endobronchial therapy. He subsequently underwent selective bronchial artery embolization, and the bleeding ceased. A CT chest revealed multiple cavitary lesions in both upper lobes. Bronchoalveolar lavage AFB smears returned positive. Based on these findings, he was started empirically on anti-tuberculous therapy, including rifampin, isoniazid, pyrazinamide and ethambutol. However, liquid medium culture grew within one week suggesting a rapidly growing mycobacterium as the likely causative microbe. At the same time, Nucleic Acid Amplification (NAA) tests for both MTB and Mycobacteria avium complex (MAC) returned negative. Therapy was hence switched to azithromycin, amikacin, and imipenem; levofloxacin was added due to ongoing suspicion for MTB. Other significant tests including HIV Antibody and Quantiferon gold were likewise negative. The patient responded to this regimen. After weeks of incubation, the AFB cultures confirmed MAC alone without a second organism. Antibiotics were ultimately switched to azithromycin, ethambutol and rifampin. DISCUSSION: This case presents a diagnostic challenge in that the patient’s rapidly growing culture and negative NAA test suggested against MAC. The clinical picture of a patient of Kenyan origin with hemoptysis and upper lobe lung disease, which is almost hallmark of MTB, further obscured the diagnosis. The significant overlap between the clinical disease manifested by various mycobacterial species makes NAA tests a particularly useful tool in guiding early treatment. They are highly accurate with a reported sensitivity and specificity of 95% and 98% in AFB-smear-positive respiratory specimens; this falls to 88% and 95% in smear-negative specimens. However, as highlighted by this case, clinicians must be vigilant of the statistical reliability of the NAA test. The false negative rate is 5% in smear positive disease, which is a small but non-negligible statistic, considering its treatment implicaitons. CONCLUSIONS: Diagnosis of mycobacterial lung disease requires microbiologic confirmation, and culture remains the gold standard test. NAA test serves as a reliable tool for rapid identification to guide early treatment. However, clinicians must be vigilant of the statistical reliability of the NAA test when adopting its use into clinical practice. Reference #1: https://academic.oup.com/cid/article/49/1/46/372207 Reference #2: http://jcm.asm.org/content/29/11/2473 Reference #3: https://academic.oup.com/cid/article/49/1/46/372207/Performance-of-Nucleic-Acid-Amplification-Tests DISCLOSURES: No relevant relationships by Yinn Shaung Ooi, source=Web Response