What is the next step for a patient with tunnel vision and a positive Rapid Plasma Reagin (RPR) test after recent treatment with doxycycline (Vibramycin) for syphilis?

Immediate Management of Suspected Ocular Syphilis

Perform a lumbar puncture for CSF examination immediately and initiate IV aqueous crystalline penicillin G 18-24 million units per day (3-4 million units IV every 4 hours or continuous infusion) for 10-14 days, as ocular syphilis is a manifestation of neurosyphilis and requires neurosyphilis treatment regardless of CSF findings. 1

Why This Patient Requires Urgent Intervention

Your patient's tunnel vision with a positive RPR after completing doxycycline treatment two months ago represents treatment failure with progression to ocular neurosyphilis—a medical emergency requiring immediate escalation of therapy. 1

Critical Actions Required

1. CSF Examination is Mandatory

• All patients with syphilitic eye disease must undergo lumbar puncture to identify CSF abnormalities, even if you plan to treat for neurosyphilis regardless of results 1
• The CSF examination establishes a baseline for monitoring treatment response through follow-up CSF examinations every 6 months until cell count normalizes 1

2. Ophthalmology Consultation

• Manage this patient in collaboration with an ophthalmologist, as recommended for all cases of syphilitic eye disease 1
• Ocular manifestations (uveitis, neuroretinitis, optic neuritis) are frequently associated with neurosyphilis 1

3. Treatment Regimen

• Primary regimen: Aqueous crystalline penicillin G 18-24 million units per day IV, administered as 3-4 million units every 4 hours or continuous infusion, for 10-14 days 1
• Alternative regimen (if IV access is problematic): Procaine penicillin 2.4 million units IM once daily PLUS probenecid 500 mg orally four times daily, both for 10-14 days 1
• After completing neurosyphilis treatment: Consider benzathine penicillin 2.4 million units IM once weekly for up to 3 weeks to provide comparable total duration of therapy as late syphilis treatment 1

Why Doxycycline Failed

While doxycycline shows similar serological treatment success rates to penicillin for early syphilis (82.9% vs 91.4%), 2 it is not adequate for neurosyphilis or ocular syphilis. The presence of ocular symptoms indicates CNS involvement requiring IV penicillin therapy. 1

Follow-Up Strategy

CSF Monitoring

• Repeat CSF examination every 6 months until cell count normalizes 1
• CSF leukocyte count is the most sensitive measure of treatment effectiveness 1
• If cell count has not decreased after 6 months, or if CSF cell count or protein is not normal after 2 years, consider retreatment 1

Serologic Monitoring

• Normalization of serum RPR titer predicts normalization of CSF parameters in immunocompetent persons 1
• Monitor RPR titers at regular intervals to assess systemic response 3

Critical Pitfalls to Avoid

• Do not delay treatment waiting for CSF results—start IV penicillin immediately upon clinical suspicion of ocular syphilis 1
• Do not use oral antibiotics (including doxycycline) for neurosyphilis or ocular syphilis—only IV penicillin is effective 1
• Do not skip the CSF examination—it is required for all ocular syphilis cases to establish baseline and guide follow-up 1
• Do not assume the positive RPR is just residual seropositivity—new neurologic or ocular symptoms mandate reassessment for active infection 3

HIV Testing

Test this patient for HIV immediately if not already done, as HIV-infected patients may be at increased risk for neurologic complications and may have higher rates of treatment failure. 1