Comparison of Pulmonary Diseases Caused by Mycobacterium Abscessus and Mycobacterium Massiliense: An Updated Analysis

Abstract RATIONALE. Despite the rising clinical importance of Mycobacterium abscessus complex pulmonary disease (PD), comparative studies between its subspecies remain limited. This study aims to compare the baseline clinical characteristics and prognosis between patients with M. abscessus and M. massiliense PD. METHODS. We retrospectively analyzed patients diagnosed with M. abscessus or M. massiliense pulmonary disease at Seoul National University Hospital from January 1st2011 to December 31th2023. Baseline characteristics, laboratory findings, radiographic features, time to progression, and treatment outcomes were compared between the two groups. RESULTS. During the study period, 347 patients were diagnosed with pulmonary diseases caused by M. abscessus (186 patients), M. massiliense (134 patients), or a mixed infection of both species (27 patients). The median age was 63 years, and 269 patients (77.5%) were female. AFB smear positivity at diagnosis was higher in M. massiliense patients (23.6%) compared to M. abscessus patients (12.4%, P=0.01). Resistance, including inducible resistance, to clarithromycin was significantly higher in M. abscessus (88.4%) than in M. massiliense (9.7%, P<0.0001) patients. A total of 99 (53.2%) M. abscessus patients and 75 (56.0%) M. massiliense patients progressed to require treatment (P=0.71), with no difference in time to progression (P=0.25). Among 146 patients treated with guideline-based therapy, 57 of 79 (72.2%) M. abscessus patients started with four or more drugs, compared to 28 of 56 (50.0%) M. massiliense patients (P=0.01), though treatment duration did not differ (P=0.36). However, the microbiological cure rate was significantly lower in M. abscessus patients (26 patients, 40.0%) than in patients with M. massiliense patients (39 patients, 81.2%) (P<0.0001). CONCLUSION. Pulmonary diseases caused by M. abscessus and M. massiliense showed no difference in progression rates or time to progression, yet the treatment success rate for M. abscessus PD was markedly lower compared to M. massiliense PD.