A 47-year-old man with a positive Rapid Plasma Reagin (RPR) test (titer of 1:64) is referred for further evaluation and treatment of syphilis. He reports having a total body rash and low-grade fever that resolved approximately 3 weeks ago. He reports new severe headaches in the past week, associated with nausea, vomiting, and mild photophobia. The headaches have not resolved with over-the-counter medications. He has not had prior testing or treatment for syphilis. A recent HIV-1/2 antigen-antibody test is negative. A lumbar puncture is performed, with cerebrospinal fluid (CSF) analysis, to evaluate for neurosyphilis.