# Granulomatosis With Polyangiitis Presenting With H1N1 Influenza

## TL;DR

A 74-year-old man with H1N1 influenza later developed a rare autoimmune disease called GPA, highlighting the need to consider autoimmune causes in unexplained lung symptoms.

## Contribution

This case report emphasizes the importance of evaluating autoimmune conditions in patients with unexplained pulmonary symptoms following viral infections.

## Key findings

- A patient with H1N1 influenza later developed GPA confirmed by elevated PR3-ANCA and renal biopsy.
- The case underscores the need for autoimmune evaluation in unexplained pulmonary symptoms.
- Treatment with corticosteroids and rituximab was required for GPA management.

## Abstract

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.