Routine laboratory tests showed elevated C-reactive protein and liver enzyme levels. Hematoxylin-eosin staining of a tissue specimen demonstrated an inflammatory infiltrate with some plasma cells. Immunohistochemical findings were positive for Treponema pallidum. Serologic results were negative for human immunodeficiency virus and hepatitis. The results for the VDRL (Venereal Disease Research Laboratory test) (1:128), TPPA (Treponema pallidum particle agglutination assay) (1:10240), and FTA-Abs (fluorescent treponemal antibody-absorption) IgG test were positive, and the level of 19S IgM FTA-Abs was marginally elevated, confirming the diagnosis of syphilis. Ocular and neurologic involvement was excluded. A chest radiograph showed an enlarged aortic contour suggestive of dilative aortic angiopathy without any signs of aneurysm. Radiographic computed tomography (CT) demonstrated thickening of the aortic wall and aortic sclerosis in the transverse plane. 18F-Fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) alongside CT (PET/CT) demonstrated a maximum isotope uptake of the descending aorta, confirming the suspected diagnosis of an aortitis (Figure 2). We thus diagnosed secondary syphilis with asymptomatic aortitis. To prevent aortic rupture triggered by massive cell disintegration of T pallidum microorganisms (Herxheimer reaction), we implemented a prophylaxis with 100-mg prednisolone prior to the antibiotic therapy with penicillin G, 6 × 5 Mio IU/d, over a 2-week period.