Anti-proteinase 3 Antibody (PR3)-Anti-neutrophil Cytoplasmic Antibody (ANCA)-Positive Vasculitis: A Rare Presentation in a 90-Year-Old Female.

Granulomatosis with polyangiitis (GPA), a rare systemic vasculitis, typically affects middle-aged adults, with incidence declining significantly in the elderly. Here, we present a rare and exceptional case of new-onset GPA in a 90-year-old female presenting with hemoptysis and characteristic systemic manifestations. Initially investigated for suspected lung malignancy due to her advancing age and history of non-Hodgkin's lymphoma (in remission since 2017), the patient was diagnosed with proteinase 3 (PR3) anti-neutrophil cytoplasmic antibody (ANCA)-positive vasculitis and characteristic imaging findings. Treatment with corticosteroids, immunosuppressants, and avacopan resulted in improved renal function and overall resolution of symptoms, highlighting the importance of considering vasculitis as a differential diagnosis in elderly patients with multisystem involvement. This case report features the diagnostic challenges and therapeutic considerations of late-onset GPA in the geriatric population.