Hidden in Plain Sight: Identifying Mycobacterium Abscessus as the Covert Cause of Chronic Lung Cavitary Lesions

Abstract Introduction: Mycobacterium abscessus complex (MABC) is the second most common nontuberculous mycobacterial infection (NTM), following Mycobacterium avium complex (MAC). MABC is characterized by significant drug resistance, limiting treatment options. The diagnostic challenges associated with cavitary lesions necessitate a comprehensive approach, as MABC can mimic malignancy, vasculitis, or pulmonary manifestations of inflammatory bowel disease (IBD). This case highlights the critical need to consider MABC in the differential diagnosis of cavitary lung lesions. Description: A 74-year-old male with history of ulcerative colitis, previously treated with Ustekinumab, presented with hemoptysis. He had known cavitary lung lesions, which were surgically resected in 2019, with nonspecific inflammatory pathology noted. Patient had recent bronchoscopy prior to admission, and CT scan at the time indicated an increase in cavitary lesions. Bronchoalveolar lavage (BAL) was negative for acid-fast bacilli (AFB) smear, MTB-PCR, cytology, and cultures. Differential diagnoses included NTM infection, vasculitis, and pulmonary IBD. Initial AFB smear revealed 3+ AFB, but subsequent smears were negative. Due to suspicion for MAC, the patient was started on Augmentin and doxycycline for two weeks. Three weeks post-discharge, cultures confirmed MABC with erm-41 gene truncation. A peripherally inserted central catheter (PICC) was placed for three months of amikacin and eravacycline infusions, alongside azithromycin and clofazimine. Discussion: Mycobacterium abscessus complex (MABC) causes severe respiratory, skin, and mucosal infections and accounts for up to 13% of pulmonary NTM cases. It is one of the most antibiotic-resistant nontuberculous mycobacteria (NTM). Diagnosing MABC is challenging as it can mimic other infections, malignancies, and autoimmune disorders, which can lead to misdiagnosis and inappropriate treatment that increases antibiotic resistance. The sensitivity of AFB smears is notably low, with some studies reporting it as low as 46%. This contribute to delays in appropriate care, as evidenced in our patient's case where diagnosis and treatment was deferred for five years. The rising antibiotic resistance complicates MABC treatment. Empiric therapy should be avoided as it may worsen resistance. While macrolides are typically used, two MABC subspecies exhibit resistance associated with the erm41 gene, which determines macrolide sensitivity. Amikacin is another mainstay of treatment, however, resistance rates are increasing. Standard management includes long-term antibiotic regimens and regular assessments, although surgical resection may be required for localized infections. Our case underscores the necessity of including MABC in the differential for patients presenting with cavitary lung lesions to expedite diagnosis and treatment, avoiding the risk for worsening antibiotic resistance.