Syphilitic bicuspid aortic valve endocarditis diagnosed by metagenomic next-generation sequencing: a case report and literature review

Background Syphilitic endocarditis, a rare complication of tertiary syphilis, poses diagnostic challenges due to the unculturable nature of Treponema pallidum and non-specific clinical manifestations. This report highlights the role of quantitative metagenomic next-generation sequencing (Q-mNGS) in confirming the diagnosis. Case Presentation A 52-year-old male patient with a bicuspid aortic valve presented with a cough and chest tightness. Serology confirmed syphilis, but blood cultures were negative. Transesophageal echocardiography revealed severe aortic regurgitation with vegetations. Q-mNGS of resected valve tissue detected T. pallidum despite negative Warthin–Starry staining. The patient underwent valve replacement and received penicillin G, with no recurrence at the 2-year follow-up. Conclusions Q-mNGS shows potentially higher sensitivity for diagnosing syphilitic endocarditis compared to traditional methods. Serological screening combined with molecular techniques is critical for culture-negative endocarditis in high-risk populations.