MPO‐ANCA‐positive granulomatosis with polyangiitis and concurrent IgG4‐related disease with periaortitis and tubulointerstitial nephritis: A case report of a new overlap syndrome?

Abstract

AbstractImmunoglobulin G4‐related disease (IgG4‐RD) is a fibroinflammatory condition that was first recognized as a unique disease entity in the early 2000s. Its diagnosis is based on specific pathologic, serologic, and clinical features, and the exclusion of several differential diagnoses, such antineutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV). However, emerging evidence suggests that these 2 conditions may overlap in some cases. Here, we report a new case of overlapping IgG4‐RD and AAV. The patient was diagnosed with IgG4‐RD owing to the presence of periaortitis and IgG4 positive tubulointerstitial nephritis. Myeloperoxidase (MPO)‐ANCA positivity, chronic paranasal sinusitis, and glomerulonephritis with granuloma led to a concurrent diagnosis of MPO‐ANCA‐positive granulomatosis with polyangiitis. Our case supports the hypothesis that diagnoses of IgG4‐RD and AAV are not mutually exclusive but can overlap. It can be assumed that an overlap with IgG4‐RD typically affects the granulomatous form of AAV, suggesting a common pathophysiological pathway for these 2 conditions.