Granulomatosis With Polyangiitis Presenting With H1N1 Influenza.

Granulomatosis with polyangiitis (GPA) is a rare antineutrophil cytoplasmic antibody (ANCA) associated vasculitis characterized by necrotizing inflammation of small- to medium-sized vessels, most commonly affecting the respiratory tract and kidneys. We report the case of a 74-year-old man who presented with H1N1 influenza infection followed by renal failure. Serologic testing revealed elevated PR3-ANCA, and renal biopsy confirmed a pauci-immune vasculitis consistent with a diagnosis of GPA requiring immunosuppressive therapy with corticosteroids and rituximab. This case highlights the necessity of a thorough evaluation for autoimmune aetiologies in patients presenting with unexplained pulmonary symptoms.