B49-16 A Complex Case of Infective Endocarditis With Mitral Valve Vegetation in Antiphospholipid Syndrome

Abstract A 45-year-old woman with a history of hypothyroidism, antiphospholipid syndrome (APLS), prior cerebrovascular accident, anemia, and polymyalgia rheumatica (PMR) presented with a two-week history of myalgias, fatigue, headache, and fevers. Upon admission, she developed hypoxemic respiratory failure requiring intubation, which was thought to be due to flash pulmonary edema and aspiration pneumonitis. Transthoracic echocardiography revealed large mitral valve vegetations associated with mitral stenosis. Blood cultures grew Streptococcus sanguinis and Haemophilus parainfluenzae, prompting treatment with vancomycin and ceftriaxone. Despite being on therapeutic anticoagulation (heparin drip), she developed a left lower extremity deep vein thrombosis, requiring thrombectomy and angioplasty. She underwent a mitral valve replacement with a mechanical valve. The excised mass, measuring 3.5 x 3.3 x 1.8 cm, was culture negative. Postoperatively, the patient improved without further embolic events or infection. No source of infection other than the mitral valve vegetations was identified. This case underscores the complexities of managing infective endocarditis (IE) in a patient with antiphospholipid syndrome (APLS), a condition that increases thromboembolic risk and complicates both diagnosis and treatment (1). The pathogens identified—Streptococcus sanguinis and Haemophilus parainfluenzae—are uncommon in IE but notable in patients with underlying valvular disease and autoimmune disorders like APLS, as both organisms can form large vegetations that embolize to distant organs (2,3). The excised mass was culture-negative, which is not unusual in IE. Tissue cultures can be negative in up to 30% of cases, particularly in those who have been pre-treated with antibiotics (4). Biofilm formation, a hallmark of IE, likely contributed to the culture negativity. Bacteria within biofilms are shielded from both antibiotics and immune responses, making them difficult to detect in tissue cultures (2). Despite negative tissue cultures, the positive blood cultures prior to surgery confirmed the active infection, highlighting the importance of blood cultures in diagnosing IE. APLS further complicates the management of IE by increasing the risk of embolic events, especially in patients with mitral valve involvement (3). This case emphasizes the need for careful anticoagulation management and a multidisciplinary approach to prevent thromboembolic complications in such high-risk patients (1,4). This abstract is funded by: none