B43-09 Unexplained Hypoxic Respiratory Failure in a 40-year-old Woman: A Case of Antisynthetase Syndrome With Nsip and Organizing Pneumonia

Abstract Background Antisynthetase syndrome (ASS) is an autoimmune disorder characterized by interstitial lung disease (ILD), myositis, and the presence of antisynthetase antibodies. The anti-PL-12 subtype often presents predominantly with pulmonary involvement, sometimes without myositis or classic systemic features. The interstitial lung disease in ASS typically demonstrates nonspecific interstitial pneumonitis (NSIP) or organizing pneumonia (OP) on pathology. Early diagnosis and immunosuppressive therapy are crucial to prevent progression to fibrosis. Case Presentation A 40-year-old woman with no significant medical history presented in March 2024 with progressive dyspnea and hypoxia. She had multiple prior admissions since February 2024 for exertional shortness of breath and diffuse bilateral ground-glass opacities on imaging. On presentation, she required supplemental oxygen. CT angiography showed extensive bilateral patchy consolidation and ground-glass opacities without pulmonary embolism.Laboratory studies revealed WBC 13.9 × 109/L, BNP 204 pg/mL, lactate 2.1 mmol/L, procalcitonin 0.05 ng/mL, and positive anti-PL-12 antibody, confirming antisynthetase syndrome. Pulmonology consultation favored NSIP versus OP. She was started on prednisone 60 mg daily, resulting in significant improvement in symptoms and oxygenation.Given persistent radiographic findings, she underwent video-assisted thoracoscopic (VATS) wedge biopsy on March 20, which revealed chronic interstitial pneumonitis with organizing pneumonia (NSIP/OP pattern). A small post-procedure pneumothorax resolved after brief chest-tube placement. She completed empiric antibiotics (Zosyn, azithromycin, amphotericin) while infection was excluded, and remained on corticosteroids with Bactrim prophylaxis. Oxygen requirements improved from high-flow nasal cannula to 2 L/min at rest and 4-6 L/min with ambulation. She was discharged on a steroid taper, furosemide 20 mg twice daily, and home oxygen. Discussion / Conclusion This case highlights anti-PL-12 antisynthetase syndrome presenting as isolated interstitial lung disease with an NSIP/OP histopathologic pattern. ASS-associated ILD may mimic infection or other inflammatory pneumonias, often delaying diagnosis. Recognition of anti-PL-12 positivity and early initiation of corticosteroids can lead to marked clinical improvement. Key learning points Anti-PL-12 ASS can present without myositis, manifesting primarily as steroid-responsive ILD.NSIP and OP are common patterns in ASS and carry a favorable prognosis with timely therapy.Multidisciplinary management (pulmonology, rheumatology, pathology) and close follow-up are essential to prevent relapse and progression to fibrosis. References: 1. Wells M et al. Front Med. 2022;9:959653. 2. Marie I et al. Chest. 2012;142(3):617-624. 3. Zanframundo G et al. Clin Exp Rheumatol. 2022;40:309-319. This abstract is funded by: None