Lambl's excrescences in a 9-year-old Japanese boy: differentiation from infective endocarditis.

Lambl's excrescences (LEs) are filiform extensions arising on the closing surface of cardiac valves, typically occurring at coaptation lines of left-sided valves. LEs are more commonly reported in adults and pediatric cases remain rare, with no previously documented cases in Japan. A 9-year-old Japanese boy initially presented with a fever and sore throat but developed right-sided neck pain several days later. Blood tests showed a white blood cell count of 33,900/mL and C-reactive protein concentration of 9.95 mg/dL. Contrast-enhanced computed tomography showed a right peritonsillar abscess, and cefotaxime and clindamycin were administered. The patient's symptoms persisted for 4 days. Therefore, he was transferred to our hospital. Transthoracic echocardiography showed trivial aortic regurgitation and a 4.4×1.0-mm filamentous structure attached to the aortic valve. The patient improved with antibiotic treatment alone, which was continued because infective endocarditis was suspected. However, transesophageal echocardiography showed no shape-like vegetations, papillary fibroelastomas, or thrombi, and repeated blood cultures were all negative, which led to a diagnosis of LEs. After completing a 3-week antibiotic course, the patient was discharged and remained asymptomatic with no structural changes in the LE in 2 years. To the best of our knowledge, this is the first report of a pediatric case of LEs associated with aortic regurgitation in Japan, highlighting that LEs should be considered in children with aortic regurgitation.