ANCA-Negative Granulomatosis With Polyangiitis Mimicking Sinusitis and Rhinoscleroma: A Case Report.

Introduction: This case details the diagnostic challenge of ANCA-negative granulomatosis with polyangiitis (GPA) initially presenting as refractory chronic rhinosinusitis, mimicking recurrent infections, and other granulomatous conditions. It highlights the potential for significant diagnostic delay when serological markers are absent. Case Presentation: A 65-year-old female with recurrent sinusitis underwent multiple antibiotic regimens and endoscopic sinus surgery. Despite this, she developed progressive destructive manifestations over 10 months: nasal septal perforation, saddle nose deformity, keratouveitis with exophthalmos, macrohematuria, and a lacunar cerebellar infarct. Serial microbiology showed various pathogens; histology initially suggested rhinoscleroma. ANCA remained negative. Interventions and Outcomes: Following the clinical diagnosis of ANCA-negative GPA, therapy with rituximab and corticosteroids was initiated, leading to significant improvement and sustained remission on maintenance immunosuppression. Conclusion: This case demonstrates that ANCA-negative GPA can present as refractory sinonasal disease. Negative serology does not exclude GPA; a high clinical suspicion is warranted in cases with destructive features and systemic progression. Early immunosuppressive treatment is essential to prevent severe organ damage.