Abstract 4372998: Mitral Mystery: A Rare Case of Nonbacterial Thrombotic Endocarditis in the Setting of Factor V Leiden

Background: Intracardiac masses present a diagnostic challenge with a broad differential that includes thrombus, tumor, and vegetation. Accurate identification is critical as management differs widely. Thrombi can mimic neoplastic or infectious masses, particularly in atypical locations or when systemic illness is absent. We present a rare case of a mitral valve thrombus in the setting of Factor V Leiden mutation, highlighting the importance of considering hypercoagulable states in the differential. Case Summary: A 75-year-old woman with a history of breast cancer, mitral insufficiency, and vascular comorbidities was found to have a 0.67 × 1.23 cm mobile mass on the ventricular surface of the anterior mitral valve leaflet during routine echocardiography. She had mild exertional dyspnea and chest discomfort but no fever or systemic signs of infection. Blood cultures, inflammatory markers, and rheumatologic workup were unremarkable. Empiric antibiotics for presumed infective endocarditis were discontinued after the clinical picture and Duke Criteria did not support infection. CT imaging showed no evidence of malignancy. Hypercoagulable testing was performed. The patient was started on warfarin following brain MRI clearance and was discharged in stable condition. Hypercoagulable studies later confirmed a Factor V Leiden mutation. At 3-week follow-up, repeat echocardiography showed complete resolution of the mitral mass. Discussion: The echocardiographic characteristics—well-circumscribed, echogenic, mobile, and ventricular-surface location—were inconsistent with vegetations or tumors. Lack of systemic illness and resolution with anticoagulation supported a diagnosis of nonbacterial thrombotic endocarditis (NBTE), or marantic endocarditis, due to Factor V Leiden. Though Factor V Leiden is a common thrombophilia, its role in intracardiac thrombus is rarely reported in adults. This case emphasizes the need to include NBTE in the differential diagnosis of cardiac masses, especially in patients with inherited thrombophilias. Conclusion: Intracardiac thrombus should be considered in patients with cardiac masses and risk factors for thrombophilia, even in the absence of infection or malignancy. This case highlights the diagnostic utility of hypercoagulable evaluation and the potential for complete resolution with anticoagulation in cases of NBTE.