Mycobacterium Avium Complex (MAC) Lung Infection Mimics Lung Cancer Nodules But Improves After Antibiotic Therapy

BACKGROUND Infection with non-tuberculous mycobacterium species commonly can present with lung nodules mimicking lung cancer on routine chest imaging leading to unnecessary invasive procedures. CASE SERIES The authors report three representative cases in which a probable Mycobacterium avium- complex (MAC) infection was discovered incidentally that mandated evaluation for a potential malignancy. After suspecting that the nodules were likely infectious and not malignant, the patients were empirically treated with azithromycin alone or in combination with other antibiotics. In each case, this treatment improved the appearance of these nodules on radiographic imaging in size, density, or both, documenting an infectious etiology thereby preventing more invasive studies and/or surgery. CONCLUSIONS These cases present typical examples of an increasingly prevalent infection commonly seen that can be mistaken for lung cancer by oncologists, particularly in endemic areas such as the Southeast U.S. Many non-malignant etiologies are capable of mimicking lung cancer including the most common, nontuberculous mycobacterium. An empiric 3-month course of azithromycin for highly suspected MAC lung infection that results in a significant reduction in the size of the nodule will verify that it is infectious and not malignant. Recognizing probable infectious lung nodules may prevent invasive, potentially morbid and expensive clinical evaluations including unnecessary surgery.