Large vessel vasculitis (LVV) in the elderly often prompts consideration of giant cell arteritis; however, mimickers must be carefully excluded. We report the case of a 70-year-old woman with constitutional symptoms, elevated inflammatory markers, and FDG-PET findings suggestive of LVV. Spontaneous clinical and laboratory improvement in the absence of immunosuppression raised suspicion for an alternative diagnosis. Further evaluation revealed positive treponemal serology, and syphilitic aortitis was confirmed. Treatment with penicillin led to complete resolution of vascular inflammation. This case highlights the importance of considering infectious mimics, such as syphilis, in atypical or self-resolving presentations of LVV, particularly in elderly patients.