BackgroundSyphilis is caused by the bacterium Treponema pallidum. Syphilis is a multistage disease, and the clinical stages of syphilis are divided to primary, secondary, and tertiary syphilis, where the tertiary stage is classified as neurosyphilis, cardiovascular syphilis, or gummatous syphilis. Here, we describe an autopsy case of acute pulmonary thromboembolism with neurosyphilis.Case presentationA male in his early 40s began to complain of hallucinations. He was admitted to a psychiatric hospital as an emergency case 4 days before death. He was physically restrained to control agitation and aggressiveness. The patient was severely obese (BMI 36.45). At autopsy, large thromboembolic masses filled the pulmonary trunk and both pulmonary arteries. Thrombi were also noted in the right popliteal vein and bilateral gastrocnemius and soleus veins, suggesting bilateral lower extremity deep vein thrombosis. Dissection of the brain, which weighed 1457 g, revealed no noteworthy macroscopic findings. Histological examination showed lymphocyte infiltration into the perivascular space of the brain tissue with no vasculitis. Immunohistochemical staining of T. pallidum was negative, the fluorescent treponemal antibody-absorption test was positive, the rapid plasma reagin titer was 1:4, and the T. pallidum hemagglutination assay titer was 1:10,240. Real-time PCR assay of the brain tissue detected low copy numbers of T. pallidum genes. Altogether, the cause of death was acute pulmonary thromboembolism resulting from bilateral lower extremity deep vein thrombosis. The patient also had early-stage meningovascular neurosyphilis.ConclusionAn autopsy case of acute pulmonary thromboembolism with meningovascular neurosyphilis is presented, including histopathological examination, serological assessment, and genetic testing. Forensic pathologists should pay attention to a myriad of syphilitic manifestations. The contributing factors for thrombosis in the present case included severe obesity, probable dehydration, and physical restraints implemented to control meningovascular neurosyphilis-induced neuropsychiatric symptoms.