Cavitary Pulmonary Disease Caused by <scp><i>Mycobacterium kyorinense</i></scp>: 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 <i>Mycobacterium tuberculosis</i> 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 <i>Mycobacterium kyorinense</i> (<i>M. kyorinense</i>) via matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). This case illustrates the pathogenic potential of <i>M. kyorinense</i> 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.