PR3-ANCA Positive Behçet's Disease with Severe Multisystem Involvement: A Diagnostic Challenge.

Background: Behçet's disease (BD) and granulomatosis with polyangiitis (GPA) are distinct vasculitides. PR3-ANCA is considered specific for GPA, yet rare BD cases demonstrate positivity, creating diagnostic dilemmas. Case Presentation: We describe a young man fulfilling criteria for BD, presenting with recurrent oral and genital ulcers, ocular inflammation, catastrophic jejunal perforations, pulmonary embolism, and myocardial infarction with non-obstructive coronary arteries. Despite strong PR3-ANCA positivity, the global phenotype was consistent with BD. Management required a complex, multimodal immunosuppressive regimen that included corticosteroids, cyclophosphamide, therapeutic plasma exchange, and rituximab. Conclusions: PR3-ANCA positivity may represent a severe BD phenotype rather than true GPA overlap, underscoring the need for individualized treatment strategies.