A rare case of non-infectious endocarditis

A 62-year-old female patient presented at the hospital with new-onset angina pectoris after tooth extraction. Due to tooth infection, a treatment with amoxicillin/clavulanic acid had already been performed. Past medical history revealed status post biological mitral valve replacement 5 years earlier as a result of endocarditis. Moreover, the patient had suffered a stroke years ago. Clinical examination was unremarkable; medication included aspirin for coronary heart disease.
Electrocardiogram was unremarkable, laboratory testing showed no signs of inflammation nor elevated cardiac enzymes. Taking the medical history with mitral valve replacement into account, transesophageal echocardiography (TOE) was performed. Flat appositions on mitral valve prosthesis without obvious valve destruction or perivalvular abscess were evident (file 1,2). The mean gradient of the mitral valve was elevated to 8 mmHg. Blood cultures detected methicillin-sensitive S. aureus.
Under the working hypothesis of infectious re-endocarditis DD thrombosis, the patient underwent an antibiotic treatment with intravenous cefazolin and anticoagulation with a DOAC. A second TOE 7 days later showed relevant progress of the mitral valve appositions despite lacking inflammatory signs in laboratory testing (file 3,4,5). PET-CT imaging failed to reveal certain evidence of endocarditis. The interdisciplinary heart team voted for re-do surgery of the mitral valve due to suspected endocarditis. The preoperative examination included a rheumatologic work-up, which identified elevated anti-cardiolipin antibodies and a positive Lupus anticoagulant. The histological specimen of the first valve replacement in 2018 was re-examined and revealed nonbacterial thrombotic endocarditis; bacterial and fungal PCR were unremarkable. Current blood cultures returned negative. Leucocyte scintigraphy could not detect any focus of inflammation.
In synopsis with blood samples, TOE and leucocyte scintigraphy findings, and a patient without fever or severe general symptoms, nonbacterial thrombotic endocarditis (NBTE) seemed most likely. As the patient developed thrombopenia after installing DOAC medication, thrombotic patterns might have adhered to the mitral valve prosthesis. The anticoagulation regime was switched to Phenprocoumon. TOE performed 6 weeks later detected manifest regressive thrombotic adherence remaining on mitral valve prosthesis, and MPG was bisected to 4 mmHg (file 6,7).
Nonbacterial thrombotic endocarditis is a rare type of aseptic endocarditis, commonly due to advanced malignancy or systemic lupus erythematodes. In some cases, inflammatory diseases like antiphospholipid syndrome, rheumatic heart disease, rheumatoid arthritis, and burns may also lead to NBTE. Characterized by the presence of thrombotic and non-infectious material on the heart valves, NBTE primarily affects the aortic and mitral valves. Patients often present with no specific symptoms until embolization occurs. Diagnostic work-up includes clinical suspicion and echocardiography (TTE, TOE). The therapeutic regime of NBTE contains treatment of the underlying disease and anticoagulation. Therefore, sustained therapeutic dose low molecular weight heparin or unfractionated heparin are recommended. The prognosis is poor owing to underlying diseases and recurrent embolic events. Especially in recurrent endocarditis, like in this clinical case, rare causes like nonbacterial thrombotic endocarditis must be taken into account.