Mitral Valve Vegetation and Embolic Stroke in Newly Diagnosed Granulomatosis with Polyangiitis: A Diagnostic Challenge Mimicking Culture-Negative Endocarditis.

INTRODUCTION: Granulomatosis with polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated small- to medium-vessel vasculitis that most commonly affects the respiratory tract and kidneys. Cardiac involvement is uncommon, and valvular manifestations are rare. Distinguishing GPA-related valvular involvement from infective endocarditis (IE) presents a significant diagnostic challenge, particularly because ANCA positivity may also occur in IE. CASE DESCRIPTION: We report a 60-year-old man who presented with necrotic lower-extremity ulcers, acute kidney injury, and elevated inflammatory markers. Serologic evaluation demonstrated positive ANCA with proteinase-3 specificity, while kidney biopsy confirmed pauci-immune necrotizing crescentic glomerulonephritis, supporting a diagnosis of GPA. Despite initiation of immunosuppressive therapy, he developed acute focal neurologic deficits, and brain magnetic resonance imaging demonstrated multifocal ischemic infarcts consistent with an embolic process. Transoesophageal echocardiography revealed a mitral valve mass with moderate-to-severe regurgitation. Blood cultures and serologic evaluation for fastidious organisms remained negative. CONCLUSION: This case highlights a rare presentation of GPA with suspected sterile valvular involvement complicated by embolic stroke and underscores the importance of distinguishing ANCA-associated vasculitis from culture-negative infective endocarditis. LEARNING POINTS: Antineutrophil cytoplasmic antibody (ANCA) positivity does not exclude infective endocarditis, as significant clinical overlap exists between these conditions.Kidney biopsy and careful microbiologic evaluation may help distinguish ANCA-associated vasculitis from infection-associated mimics.Cardiac imaging should be considered in patients with granulomatosis with polyangiitis who develop unexplained focal neurologic deficits.