Abstract Introduction Antineutrophil cytoplasmic antibody-associated interstitial lung disease (ANCA-ILD) is an uncommon but increasingly recognized complication, most often associated with myeloperoxidase (MPO)-ANCA and microscopic polyangiitis (MPA). The reported prevalence of ANCA positivity among idiopathic interstitial pneumonias ranges between 4-10%, with 20-45% of patients developing systemic vasculitis over time. ILD may precede vasculitis with pulmonary fibrosis being the only manifestation in some patients. Coexistence of ANCA-associated disease and large-vessel vasculitis such as giant cell arteritis (GCA) is extremely rare, limited to isolated case reports. Case Presentation An 82-year-old female with biopsy-proven GCA diagnosed in 2015 and established ILD was admitted for elective total knee replacement, complicated with acute hypoxic respiratory failure due to Pneumocystis jirovecii pneumonia (PJP). She was discharged on supplemental oxygen and later established care with our ILD clinic. Review of prior records revealed a diagnosis of P-ANCA-associated ILD with a usual interstitial pneumonitis (UIP) pattern eight years prior, managed with rituximab maintenance therapy, achieving stable lung function and minimal radiologic progression for several years until recent hospital admission. She never had systemic ANCA-associated vasculitis features.Seven months before this admission, pulmonary function tests (PFTs) showed FVC 2.14 L (93%), FEV1 1.65 L (94%), and DLCO 11.14 (64%), and she was on room air. After recovery from pneumonia, repeat CT and PFTs demonstrated progressive fibrosis with a decline in lung function (FVC 1.31 L; FEV1 1.15 L) and increased oxygen requirement. Rituximab was discontinued due to hypogammaglobulinemia and prior PJP infection. Immunosuppressive and anti-fibrotic therapy was initiated, and currently she remains on prednisone 5 mg daily, mycophenolate 720 mg twice daily, and pirfenidone 267 mg three times daily, with continuous oxygen (4-6 L/min). Follow-up PFTs six months later showed stable function (FVC 1.33 L; FEV1 1.02 L). Discussion While GCA-related lung disease has been described, a fibrotic UIP pattern is exceedingly rare, as GCA typically manifests with granulomatous inflammation or nodular infiltrates. This patient’s MPO-ANCA-positive ILD likely represents an ANCA-associated fibrotic process distinct from GCA-related ILD. Surgical stress, anesthesia, and mechanical ventilation have been recognized as potential precipitants of ILD exacerbation, likely through immune activation, oxidative stress, and alveolar injury, while infection can further accelerate progression. This case highlights the complexity of diagnosing and managing ILD in patients with overlapping autoimmune disorders. Recognition of ANCA-ILD, even in the absence of systemic vasculitis, is essential given its progressive course and poor prognosis despite immunosuppression and antifibrotic therapy. This abstract is funded by: none
Zubairi et al. (Fri,) studied this question.