A35-04 Pulmonary-limited MPO-ANCA Vasculitis Presenting as a Solitary PET-avid Pulmonary Nodule

Abstract Introduction Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) typically affects small vessels in multiple organs, with myeloperoxidase (MPO)-ANCA vasculitis frequently involving the kidneys and lungs. Pulmonary manifestations usually include diffuse alveolar hemorrhage or interstitial lung disease. Nodular pulmonary disease is uncommon and, if present, generally multiple. Solitary pulmonary nodules as the initial manifestation of MPO-ANCA vasculitis are exceedingly rare. We present one such case of MPO-ANCA vasculitis presenting as a malignancy mimic. Description of Case A 71-year-old man with chronic obstructive pulmonary disease (COPD), a 45-pack-year smoking history, and occupational exposure to concrete dust, underwent routine lung cancer screening. Imaging revealed a new 9 × 8.5 × 6.5 mm spiculated right upper lobe nodule. Positron emission tomography (PET) demonstrated intense hypermetabolic activity in the pulmonary nodule, with mild uptake in hilar and mediastinal lymph nodes, raising concern for primary lung malignancy. The patient underwent robotic navigational bronchoscopy with endobronchial ultrasound (EBUS). Transbronchial needle aspiration (TBNA) and multiple biopsies of the right upper lobe nodule demonstrated necrotizing granulomatous inflammation with palisading histiocytes and areas of fibrosis and hemorrhage. Stains for acid-fast bacilli and fungi were negative. Cytology and lymph node biopsies showed no malignancy. The above findings were confirmed by an external second opinion and subsequent repeat bronchoscopy with bronchoalveolar lavage (BAL) and histopathological evaluation.Extensive serologic testing revealed positive p-ANCA and elevated MPO antibody, confirmed on repeat testing. Other autoimmune markers, including PR3-ANCA, ANA, anti-dsDNA, and complement levels, were within normal limits. Renal function was normal, urinalysis was unremarkable, and there was no evidence of systemic involvement. A diagnosis of pulmonary-limited MPO-ANCA vasculitis was made. The patient was referred to rheumatology and initiated on immunosuppressive therapy, remaining clinically stable with only baseline COPD symptoms. Discussion This case represents an unusual presentation of MPO-ANCA vasculitis as a solitary pulmonary nodule, a phenotype typically associated with granulomatosis with polyangiitis (GPA, PR3-ANCA). Initial radiographic and PET features, such as in this case, can closely mimic malignancy. Multidisciplinary evaluation, including histopathology, serology, and exclusion of infection, was essential for accurate diagnosis. Awareness of this phenotype is crucial for clinicians evaluating solitary nodules, emphasizing the need for integrated imaging, histopathologic, and serologic assessment. Recognition is critical to allow timely immunosuppressive therapy, potentially preventing progression to systemic disease or irreversible lung injury. This abstract is funded by: None