A 59-year-old woman with right breast cancer presented to our department with suspicion of NTM infection based on abnormal lung opacities that had been detected 2 years ago. Because she had no respiratory symptoms and the opacities remained stable, she was initially monitored without medication. She underwent right breast resection, followed by treatment with paclitaxel and human epidermal growth factor receptor 2 monoclonal antibodies for 1 year, as well as radiation therapy (50 Gy) to the right chest. However, during chemotherapy for breast cancer, the lung opacities progressed and a cavitary mass was detected (Fig. 1, Fig. 2). Therefore, she underwent further examinations.
Upon examination, she was asymptomatic and had normal vital signs. Staining and culture of three sputum samples, including for acid-fast bacteria, did not reveal evidence of bacterial infection. Additionally, interferon-gamma release assay (T-SPOTR; BML, Tokyo, Japan) yielded negative results. Bronchioalveolar lavage fluid via bronchoscopy and sputum samples were collected. Following a 6-week incubation period in a liquid medium, acid-fast staining and culture of the bronchioalveolar lavage fluid showed bacterial growth. However, polymerase chain reaction testing of the samples showed no growth of M. tuberculosis, M. avium, or Mycobacterium intracellulae. As a result, M. shinjukuense was diagnosed by mass spectrometry (MALDI-Biotyper, Bruker Daltonics, Bremen, Germany).
Based on the worsening lung opacities, treatment was initiated for our patient based on 10 previous reports of 16 cases of M. shinjukuense (Table 1). Among these cases, eight were treated with anti-tuberculous drugs, one with erythromycin, one with CLA followed by anti-tuberculous drugs, one with RFP, levofloxacin, and CLA, and three with RFP, EB, and CLA.
In our patient, the minimum inhibitory concentrations (MICs) of CLA, RFP, EB (BrothMIC NTM, Kyokuto Pharmaceutical Industrial Co., Ltd., Tokyo, Japan), and INH (Vit spectrum-SR, Kyokuto Pharmaceutical Industrial Co., Ltd.) using the broth microdilution method were <0.03, <0.03, <1, and <0.02 mug/mL, respectively. In our study, the MIC of CLA was similar to that of the cases 5 and 14previously reported (Table 1) (3, 9). We treated our patient with RFP, EB, and CLA instead of RFP, EB, and INH because of the more common side effects with INH than CLA. The initial treatment included 600 mg/day of CLA, 500 mg/day of EB, and 300 mg/day of RFP. The patient weighed 48 kg, and no side effects were observed during the first month of treatment. Therefore, we increased the dose of CLA to 800 mg/day and continued EB and RFP at the same doses. After 6 months of treatment initiation, the sputum culture was negative for acid-fast bacilli. Due to the presence of a cavitary lesion and the absence of an established treatment duration for this regimen, we continued treatment for 2 years, similar to previous cases of M. avium complex, to ensure mycobacterial elimination. After 2 years of treatment, the nodules and fibrocavitary disease significantly improved (Fig. 3).