Abstract Introduction Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a rare, life-threatening autoimmune disease causing necrotizing small-vessel inflammation, most often involving the lungs and kidneys, leading to diffuse alveolar hemorrhage and glomerulonephritis. Although ANCA testing is central to diagnosis, approximately 10-20% of patients may initially test negative, delaying recognition and treatment. Early identification and immunosuppression are critical, as advanced interventions such as extracorporeal membrane oxygenation (ECMO) or lung transplantation may be unfeasible in critically ill patients. Case Description A 54-year-old woman with a 10-pack-year smoking history and newly diagnosed interstitial lung disease (ILD) with possible idiopathic pulmonary fibrosis presented with one week of worsening dyspnea. She was recently hospitalized for bilateral pneumonia complicated by acute respiratory distress syndrome (ARDS) and idiopathic pulmonary fibrosis requiring mechanical ventilation. Infectious and autoimmune workup, including antinuclear antibody (ANA), ANCA, and bronchoscopy, was unrevealing. Chest computed tomography showed bilateral ground-glass opacities, reticulation, and lower-lobe honeycombing. After improvement, she was discharged on prednisone and home oxygen but readmitted within a week for worsening hypoxemia. CT angiography excluded pulmonary embolism but revealed bilateral consolidations and fibrotic evolution. She was admitted to the ICU with acute hypoxemic respiratory failure and sepsis, intubated on hospital day 1, and treated with antibiotics, corticosteroids, fluids, and vasopressors. Due to hemodynamic instability and critical condition, lung biopsy was deferred, and transplant evaluation was declined. She received mycophenolate, pulse-dose steroids, and rituximab without improvement. By day 10, she developed rapidly progressive kidney injury with nephritic sediment and red blood cell casts, prompting repeat immunologic testing, including cytoplasmic ANCA. Despite maximal support, deep sedation, and prone positioning for refractory hypoxemia, her condition progressed to ARDS with multiorgan failure. After multidisciplinary discussions, the family elected to transition to comfort care. After her death, repeat serologic results became available and revealed a new ANCA-positive result with C-ANCA positivity (1:40), confirming AAV. Discussion This case demonstrates the diagnostic and therapeutic challenges of AAV presenting as ARDS with delayed ANCA positivity—a rare and life-threatening manifestation. The initially seronegative presentation that later converted to positive during deterioration emphasizes that early negative results do not exclude AAV. The coexistence of ILD, ARDS, and vasculitis highlights diagnostic complexity, as inflammatory injury may mimic infection or ILD exacerbation. Clinically, this case reinforces maintaining suspicion for AAV in critically ill patients with pulmonary-renal involvement, considering empiric immunosuppression even without serologic confirmation, and evaluating early for ECMO or transplantation before multiorgan dysfunction limits options. This abstract is funded by: none
Aung et al. (Fri,) studied this question.
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