## **Core Concept**
The patient presents with primary syphilis complicated by neurosyphilis, indicated by meningitis. The treatment for syphilis, especially in its neurosyphilis stage, involves antibiotics, typically penicillin. Monitoring the effectiveness of treatment is crucial.

## **Why the Correct Answer is Right**
For neurosyphilis, the standard treatment is intravenous penicillin G for 10-14 days. Monitoring the treatment response is critical and involves **serological tests**, specifically the Venereal Disease Research Laboratory (VDRL) test, which is a non-treponemal test. This test is used to monitor the response to treatment, with titers expected to decrease over time if the treatment is effective.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While imaging studies might be used initially to assess for complications of neurosyphilis, they are not the primary method for monitoring treatment response.
- **Option B:** CSF pleocytosis (increase in cells in the cerebrospinal fluid) is an indicator of neurosyphilis but is not typically used to monitor treatment response over time; rather, it's a diagnostic criterion.
- **Option C:** There is no widely recognized or standard test labeled simply as "serum RPR" that is exclusively used for monitoring; however, RPR (Rapid Plasma Reagin) is similar in concept to VDRL and used for screening.
- **Option D:** Although treponemal tests (like FTA-ABS) can remain positive for life, they are not typically used to monitor treatment efficacy.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **non-treponemal tests (VDRL/RPR)** are used for monitoring the response to treatment in syphilis. A four-fold decrease in titers (or a decrease by two dilutions) is considered a good response to treatment.

## **Correct Answer:** D. **Monitoring with VDRL (or RPR) test titers in serum and CSF**.