Pulmonary Nontuberculous Mycobacterial Disease in a Tuberculosis-Endemic Setting: Two Cases Illustrating Diagnostic Pitfalls

Background and Clinical Significance: Pulmonary disease caused by nontuberculous mycobacteria (NTM) represents an important diagnostic challenge in tuberculosis-endemic settings because its clinical, radiological, and microbiological features may overlap with those of pulmonary tuberculosis (TB). Accurate distinction between these conditions is essential to avoid diagnostic delay and inappropriate treatment. Case Presentation: We present two cases that illustrate the heterogeneity of imaging patterns associated with NTM disease. The first case involved a 55-year-old woman with previously treated pulmonary tuberculosis who presented with chronic productive cough, recurrent mild hemoptysis, and progressive nodular-bronchiectatic and cavitary abnormalities. Mycobacterium avium was repeatedly isolated from independently collected respiratory specimens and identified using a line probe assay (LPA). The second case involved a 65-year-old man with severe chronic obstructive pulmonary disease (COPD), bronchiectasis, previous tuberculosis, and extensive bilateral fibrocavitary lung disease. Respiratory specimens were acid-fast bacilli-positive, whereas GeneXpert MTB/RIF repeatedly failed to detect the Mycobacterium tuberculosis complex. Repeated cultures identified Mycobacterium xenopi, including isolates from two sputum specimens and one bronchial aspirate. Treatment was subsequently adapted according to species identification and multidisciplinary assessment. These cases illustrate two major phenotypes of pulmonary NTM disease: nodular-bronchiectatic disease caused by M. avium and fibrocavitary disease caused by M. xenopi. They emphasize that persistent acid-fast bacilli (AFB) positivity with negative GeneXpert MTB/RIF results should prompt consideration of NTM alongside other differential diagnoses, followed by mycobacterial culture and species-level identification. Conclusions: The diagnosis of pulmonary NTM disease requires integration of clinical manifestations, radiological evolution, and repeated microbiological confirmation. Early species identification, multidisciplinary treatment selection, and close follow-up may reduce diagnostic delays and support appropriate individualized management.