Refractory mastoiditis as the initial manifestation of granulomatosis with polyangiitis:a case report and literature review.

Background: Granulomatosis with Polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis that predominantly affects the upper or lower respiratory tracts and the kidney. While otologic involvement is relatively common in GPA, isolated destructive mastoiditis as the initial manifestation is exceedingly rare, often leading to misdiagnosis. Case presentation: A 69-year-old female presented with a 3-months history of progressive bilateral hearing loss and otorrhea. Based on clinical and radiological findings, she was initially diagnosed with acute mastoiditis but showed no response to antibiotic therapy. She subsequently underwent right sided canal-wall-up mastoidectomy; however, postoperative symptoms persisted, and pathological examination only revealed inflammatory granulation tissue. Her condition further deteriorated, with the development of contralateral ear involvement and persistent low-grade fever. Serological testing eventually showed a proteinase 3 antineutrophil cytoplasmic antibodies (PR3-ANCA) level>200 RU/mL and chest computed tomography (CT) demonstrated multiple bilateral pulmonary nodules. The patient was thus diagnosed with GPA and initiated on methylprednisolone pulse therapy, followed by rituximab (RTX). Conclusion: This case highlights that, in patients with refractory mastoiditis unresponsive to conventional antibiotics and surgical intervention, otolaryngologists should maintain a high index of suspicion for underlying systemic vasculitides and initiate early ANCA testing. Such measures are critical to avoid diagnostic delays and prevent irreversible organ damage.