A Patient with Granulomatosis with Polyangiitis Presenting with Abdominal Pain and IgA Deposition in Cutaneous Vessel Walls, Mimicking IgA Vasculitis

Introduction: Granulomatosis with polyangiitis (GPA) and IgA vasculitis are both capable of causing rapidly progressive glomerulonephritis (RPGN) and purpura. Characteristic manifestations of GPA include sinusitis, pulmonary and kidney involvement, accompanied by elevated PR3-ANCA titers, while abdominal pain is uncommon. We present a case of GPA that manifested with abdominal pain and IgA deposition in the walls of cutaneou vessels, complicating the diagnostic. Case Description: A 61-year-old man with a one-year history of chronic sinusitis presented with fever, palpable purpura on the lower extremities, abdominal pain, and glomerular hematuria. Computed tomography revealed pulmonary nodules, kidney enlargement, and diffuse small intestinal wall thickening. Skin biopsy demonstrated necrotizing vasculitis with associated granulomatous inflammation and IgA deposition within the vessel walls, indicative of IgA vasculitis. Oral prednisolone was started, but within a week, kidney function deteriorated rapidly, with serum creatinine rising from 1.0 mg/dL to 6.3 mg/dL, requiring hemodialysis. Laboratory tests revealed a markedly elevated PR3-ANCA level (315 U/mL). Kidney biopsy demonstrated cellular crescents in 50% of glomeruli, without significant IgA deposition. Based on the clinical and pathological findings, the patient was diagnosed with GPA. The patient was treated with high-dose intravenous steroids, avacopan, rituximab, and plasma exchange therapy. Following treatment, kidney function improved with serum creatinine decreasing to 1.7 mg/dL, allowing discontinuation of dialysis. The purpura and intestinal wall thickening also resolved. Discussion: Notably, the patient presented with abdominal pain and IgA deposition in cutaneous vessels, complicating the differentiation between GPA and IgA vasculitis. There have been only a limited number of reported cases of GPA mimicking IgA vasculitis in pediatric patients, and this is the first report in adults. Gastrointestinal involvement is observed in only 5% to 10% of GPA cases. IgA deposition on the skin in cases of GPA was reported to be attributed to the presence of circulating immune complexes. In cases of RPGN with IgA deposition on the skin and concurrent abdominal pain, GPA and IgA vasculitis should be considered as potential diagnoses.