Abstract Introduction Organizing pneumonia (OP) is a histopathologic pattern of lung injury defined by intraluminal plugs of granulation tissue (Massonbodies) within distal airspaces and alveolar ducts. Interstitial lung disease (ILD) occurs in approximately 30-40% of patients with polymyositis, mostoften with a nonspecific interstitial pneumonia (NSIP) pattern. Biopsy-proven OP within inflammatory myopathies is uncommon and may beradiographically indistinguishable from infection, drug-induced pneumonitis, or progression of chronic ILD. This case underscores the diagnostic andtherapeutic importance of recognizing OP as a potentially reversible manifestation of polymyositis-associated ILD. Case Presentation A 62-year-oldwoman with polymyositis diagnosed in 1995, based on proximal muscle weakness, elevated creatine kinase, and electromyographic findings, achievedremission following a course of prednisone and methotrexate. Decades later, coronary calcium screening incidentally revealed subpleural reticularchanges consistent with early ILD. The patient was asymptomatic and declined further testing. One year later, she developed exertional dyspnea and adry cough. High-resolution CT demonstrated patchy bilateral consolidation and ground-glass opacities on a background of mild fibrotic change.Differential considerations included infection, drug-induced pneumonitis, and autoimmune ILD flare. Bronchoscopy with transbronchial biopsyrevealed multiple foci of intra-alveolar fibroblastic plugs consistent with organizing pneumonia. No viral inclusions, fungal elements, or mycobacterialorganisms were identified. Serologic testing showed a positive ANA titer of 1:320 with a negative extended myositis antibody panel. The patient wastreated with systemic corticosteroids followed by steroid-sparing therapy with mycophenolate mofetil. Six-month follow-up CT demonstrated near-complete resolution of airspace disease, leaving only minimal linear scarring and mild subpleural fibrosis. After pulmonary rehabilitation, she reportedmarked improvement in exercise tolerance and remained clinically stable at one year on low-dose prednisone and maintenance mycophenolate. Discussion Polymyositis-associated ILD typically presents as NSIP. Biopsy-confirmed OP is rare but important to identify because it is frequentlycorticosteroid-responsive and potentially reversible. Radiologic overlap with infection or drug-induced pneumonitis often delays immunosuppression,risking progression to fibrosis. When noninvasive evaluation is inconclusive, transbronchial biopsy can provide a definitive diagnosis that guidesmanagement and avoids unnecessary antimicrobial exposure. Conclusion This case illustrates that OP may represent a distinct, reversible phenotypewithin polymyositis-associated ILD. Histologic confirmation remains essential when clinical and imaging findings are ambiguous, as timely recognitionand immunosuppressive therapy can restore pulmonary function and prevent irreversible fibrotic remodeling. This abstract is funded by: None
Fuesser et al. (Fri,) studied this question.