Nontuberculous mycobacterial pulmonary disease: Epidemiology, prognostic determinants, and implications for treatment decision.

The global burden of nontuberculous mycobacterial pulmonary disease (NTM-PD) continues to increase, particularly in East Asia, including Japan. Although epidemiological understanding has expanded, the clinical course of NTM-PD remains highly heterogeneous and is influenced by host immunity, structural lung abnormalities, comorbidities, and environmental factors. Determining the optimal timing for initiating treatment remains challenging, particularly in cases of non-cavitary or mild disease. Recent evidence has elucidated several key prognostic determinants, including cavitary disease, infecting species such as Mycobacterium intracellulare or M. abscessus, and markers of poor nutritional status, such as low body mass index. These factors help identify patients who may benefit from early interventions. Despite the availability of antimicrobial therapy, significant risks of drug toxicity and macrolide resistance necessitate careful consideration before administering treatment to all patients. Consequently, watchful waiting is crucial for carefully selected patients, serving either as conservative management when treatment risks outweigh benefits or as active surveillance when the risk of short-term progression is low. Several prognostic scoring systems, including the BACES, MAC prognostic, and Bronchiectasis and Cavity Distribution scores, provide support for objective risk stratification and clinical decision-making across diverse patient groups. By integrating available evidence, this review delineates how host susceptibility, microbial characteristics, radiological patterns, and comorbidity-related factors collectively influence disease development, progression, and prognosis. Continued efforts to refine risk stratification, incorporate microbiological and immunological markers, and validate prediction models across populations are essential for advancing individualized management and improving long-term outcomes in patients with NTM-PD.