Pseudotumoral Pulmonary Mycobacterium avium Disease in a Patient on Ruxolitinib Therapy

Pulmonary disease caused by nontuberculous mycobacteria represents an important diagnostic challenge, particularly in immunocompromised patients, in whom clinical and radiologic findings may mimic malignancy. We report the case of a 70-year-old woman with myelofibrosis treated with ruxolitinib who developed a tumor-like lesion in the left upper lobe on computed tomography, highly suggestive of lung cancer. Despite broad-spectrum antibiotic therapy, the lesion persisted; bronchoscopy did not yield diagnostic findings, and CT-guided transthoracic biopsy demonstrated necrotizing granulomatous inflammation without evidence of malignancy. Microbiological analysis subsequently identified Mycobacterium avium, and targeted antimycobacterial therapy led to clinical and radiologic improvement. This case highlights that pulmonary nontuberculous mycobacterial infection may present as a pseudotumoral lesion and should be considered in the differential diagnosis of mass-like pulmonary opacities, particularly in patients receiving Janus kinase inhibitor therapy.