Mycobacterium avium complex pulmonary disease in rheumatoid arthritis-associated interstitial lung disease under non-biologic immunomodulatory therapy: A case report

RATIONALE: Rheumatoid arthritis (RA) is a well-recognized risk factor for nontuberculous mycobacterial infections, especially among patients receiving glucocorticoids or biological disease-modifying antirheumatic drugs. However, cases of Mycobacterium avium complex (MAC) pulmonary disease in RA patients without such immunosuppressive therapies are rarely reported, which challenges the conventional risk stratification. PATIENT CONCERNS: A 78-year-old male with a 3-year history of RA and interstitial lung disease (ILD) presented with progressive dyspnea and chest tightness. He had no fever, joint swelling, or typical infection flares. Before admission, he was treated with Tripterygium Glycosides and Iguratimod (non-biologic, non-glucocorticoid agents). DIAGNOSIS: The patient had chest tightness and weight loss. Chest high-resolution computed tomography showed asymmetric progression of ILD, along with tree-in-bud signs, centrilobular nodules, and suspicious fibrocavities. Bronchoscopy revealed necrotizing granulomatous inflammation, and quantitative metagenomic sequencing of bronchoalveolar lavage fluid confirmed MAC (no drug-resistant genes detected). INTERVENTIONS: The patient was put on a 4-drug anti-MAC regimen (rifampicin, azithromycin, ethambutol, amikacin). However, he was lost to follow-up after being transferred to a tuberculosis specialist hospital. He eventually died of unknown causes, and there were prior reports of his nonadherence to treatment. OUTCOMES: For RA patients with ILD who show asymmetric imaging progression or discordant inflammatory markers, it is crucial to actively screen for atypical pathogens like MAC, even in the absence of glucocorticoid or biologic exposure. This case highlights the necessity of expanding nontuberculous mycobacterial infection risk assessment beyond traditional immunosuppressive therapies in RA-ILD patients. LESSONS: For patients with autoimmune disease-associated interstitial pneumonia, particularly those with progressive interstitial lung disease (ILD) despite stable autoimmune serology, proactive screening for atypical pathogens such as nontuberculous mycobacteria is critical. When imaging shows asymmetric lesions, tree-in-bud opacities, centrilobular nodules, or fibrocavitary changes, clinicians should prioritize comprehensive etiological evaluation - including bronchoscopy and histopathology - to avoid misdiagnosing these opportunistic infections.