Asymptomatic pulmonary Mycobacterium heckeshornense infection detected by routine health screening.

Mycobacterium heckeshornense is a rare nontuberculous mycobacterium that has been reported sporadically since its first description by Roth et al. in 2000. From the earliest reports, infections have been documented not only in immunocompromised patients or those with underlying lung disease, but also in immunocompetent individuals, with a wide range of clinical manifestations. However, owing to the limited number of cases and their heterogeneity, the full clinical spectrum of this organism has not been clearly defined. We report a case of asymptomatic pulmonary M. heckeshornense infection in a healthy 48-year-old man, incidentally detected by an abnormal chest radiograph during routine health screening. Chest computed tomography revealed a cavitary lesion in the left lower lobe and centrilobular nodules in the right middle lobe. Bronchoscopy demonstrated acid-fast bacilli, and M. heckeshornense was identified from sputum and bronchial lavage cultures using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Treatment with clarithromycin, rifampicin, and ethambutol resulted in marked radiographic improvement. By integrating this case with previously reported pulmonary infections in immunocompetent hosts, we demonstrate that M. heckeshornense infection encompasses a broad clinical spectrum ranging from highly destructive disease requiring surgical intervention to long-standing, subclinical infection. The present case represents the most indolent phenotype reported to date and underscores the importance of considering this rare pathogen even in asymptomatic, immunocompetent individuals.