Abstract Introduction Organizing pneumonia (OP) represents a distinct pattern of lung injury marked by intra-alveolar granulation tissue within distal airways and alveolar ducts. It may arise idiopathically or secondarily from autoimmune disease, infection, medications, or malignancy. Pulmonary complications are well recognized in connective tissue diseases, yet OP as a manifestation of mixed connective tissue disease (MCTD) remains uncommon. Because clinical and radiographic features often resemble infection or other interstitial lung diseases (ILD), early recognition is essential to guide immunosuppressive therapy and prevent fibrotic progression. Case Presentation A 74-year-old woman with systemic lupus erythematosus (SLE) and atrial fibrillation on amiodarone presented with two weeks of malaise, dry cough, diffuse myalgias, and progressive dyspnea. On admission, she required 10-15 L/min of oxygen via oxymizer. Physical examination revealed mild sclerodactyly, bilateral hand swelling, and fine bibasilar crackles. Serologic testing demonstrated a positive ANA with high-titer anti-RNP, anti-SSA, and anti-chromatin antibodies. Anti-Smith antibody was negative, complement levels were normal, and an extended myositis panel was negative. Repeat studies confirmed persistent anti-RNP and anti-SSA positivity. High-resolution chest CT revealed asymmetric right-predominant ground-glass and reticular opacities with mild left upper lobe involvement and a trace right pleural effusion. Given her serologic profile, cutaneous findings, and pulmonary pattern, MCTD with secondary organizing pneumonia and possible connective tissue disease-associated interstitial lung disease was suspected. The patient was treated with high-dose corticosteroids and initiated on mycophenolate mofetil. Empiric antibiotics were administered for possible superimposed infection. Lung biopsy was deferred due to ongoing oxygen requirements. She improved clinically, though remained oxygen-dependent at discharge. At six-month follow-up, she reported significant symptomatic improvement and was ambulating on 1 L oxygen via nasal cannula. Discussion MCTD is defined by overlapping clinical features of SLE, systemic sclerosis, and polymyositis, and is characterized by high-titer anti-RNP antibodies. Pulmonary involvement most often occurs as interstitial lung disease (50-66%) exhibiting nonspecific interstitial pneumonia and/or OP patterns. OP typically presents subacutely with cough, dyspnea, and patchy opacities on imaging. Distinguishing it from infection, amiodarone pneumonitis, or other ILDs can be challenging. However, OP is often highly responsive to corticosteroids, with rapid clinical and radiographic improvement once therapy is initiated. Conclusion This case highlights OP as a rare pulmonary manifestation of MCTD. In patients with anti-RNP positivity and features such as sclerodactyly and inflammatory arthritis, MCTD-associated OP should be considered. Early recognition and prompt immunosuppressive therapy are critical to optimize recovery and prevent progression to fibrosis. This abstract is funded by: None
Fuesser et al. (Fri,) studied this question.