Cavitary Pulmonary Disease Caused by <i>Mycobacterium kyorinense</i>: A Case Report on a 3-Year Clinical Course

An 80-year-old female presented with haemoptysis, and chest computed tomography (CT) revealed bronchiectasis in the right middle lobe accompanied by granular and nodular opacities in the right lower lobe. Although acid-fast bacilli (AFB) smears were consistently positive, polymerase chain reaction (PCR) assays for Mycobacterium tuberculosis yielded negative results, and repeated sputum cultures on conventional solid-phase media failed to identify the causative organism. Cavitary pulmonary lesions developed progressively over 3 years, accompanied by persistent AFB smear positivity. Ultimately, liquid culture using the Mycobacteria Growth Indicator Tube (MGIT) system isolated nontuberculous mycobacteria, subsequently identified as Mycobacterium kyorinense ( M. kyorinense ) via matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). This case illustrates the pathogenic potential of M. kyorinense to induce cavitary pulmonary disease in otherwise healthy individuals, underscoring the necessity of early diagnostic strategies and prompt therapeutic intervention to prevent irreversible pulmonary damage.