Abnormal cortical amyloid deposition in ¹⁸F-Florbetapir PET/CT: General paresis of the insane mimicking early-onset Alzheimer's disease.

General paresis (GP) is a type of neurosyphilis characterized by progressive memory impairment and mental disorders. It exhibits clinical, neuroimaging, and pathological similarities to Alzheimer's disease (AD). Here, we report a 37-year-old man with memory impairment and emotional disorders, who was clinically diagnosed with neurosyphilis, specifically GP. The fluorine-18 (¹⁸F)-Florbetapir positron emission tomography/computed tomography (PET/CT) of the patient showed mild diffuse amyloid deposition in both the cerebral and cerebellar cortex. Moreover, hypermetabolism in the left hippocampal region was revealed on ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET/CT. The patient's cerebrospinal fluid (CSF) test and genotyping results further excluded coexistent genetic AD. This case highlights the significance of considering neurosyphilis as a possible differential diagnosis in dementia patients with atypical positive amyloid PET findings. The mechanisms underlying aberrant amyloid deposition in neurosyphilis require further investigation.