Biopsy-Proven Non-glomerular Renal Pathology in Localized Granulomatosis With Polyangiitis Treated With Methotrexate and Avacopan Presenting With New Renal Symptoms: A Case Report

Granulomatosis with polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis that commonly involves the upper respiratory tract and kidneys. The development of new-onset urinary abnormalities, microscopic hematuria, and declining renal function in a patient on treatment with methotrexate and avacopan warrants a prompt renal biopsy to lead management decisions. We describe a case of localized sinonasal GPA in a patient receiving methotrexate and avacopan who presented with new renal symptoms. Laboratory evaluation revealed a serum creatinine of 1.4 mg/dL and a urine protein-creatinine ratio (UPCR) of 0.96 g/g with moderate hematuria and red blood cell casts on urine microscopy. Renal biopsy revealed no evidence of pauci-immune crescentic glomerulonephritis, highlighting the importance of histopathologic confirmation before escalation of immunosuppressive therapy. These findings prevented escalation to stronger immunosuppressive therapy and allowed continuation of the existing regimen. Moreover, the combined use of methotrexate and avacopan in nasal-limited GPA is not well documented, and this case adds more clinical understanding to this therapeutic strategy.