Syphilis complicated with pericardial effusion: a case report.

BACKGROUND: Pericardial effusion is a relatively common clinical condition that can be classified into inflammatory and non-inflammatory types, with infection being the most frequent cause. However, syphilis as an etiological factor remains extremely rare. CASE PRESENTATION: A 76-year-old male was admitted to the hospital due to progressive dizziness and exertional dyspnea. Initial evaluation revealed moderate anemia, elevated inflammatory markers, and imaging-confirmed moderate-to-large pericardial effusion. Despite blood transfusions and empirical therapies (nerve nutrition, diuretics, antibiotics), persistent low-grade fever and worsening effusion necessitated pericardiocentesis, draining 220 mL of light red hemorrhagic exudate. Pericardial fluid analysis demonstrated exudative features, with negative cultures. Notably, syphilis serology revealed strongly positive results (syphilis-specific antibodies 436.62 COI; toluidine red unheated serum test 1:32), further confirmed by elevated syphilis-specific antibodies in pericardial effusion (555.64 COI). The patient denied high-risk sexual behaviors and exhibited no typical syphilitic lesions. After excluding malignancies, autoimmune diseases, and other transmitted infections, latent syphilis complicated with pericardial effusion was diagnosed. Unfortunately, robust evidence, including PCR and histopathological biopsy, is lacking to support the hypothesis that syphilis directly infects the pericardium and leads to pericardial effusion. Treatment with penicillin resulted in the resolution of symptoms and pericardial effusion, with no subsequent recurrence. CONCLUSION: This presentation recommends syphilis testing in patients with unexplained or recurrent pericardial effusions, after excluding more common causes.