Evaluation of an automated rapid plasma reagin test of serum and cerebrospinal fluid for monitoring neurosyphilis treatment: a case report

This case report explores the utility of monitoring automated rapid plasma reagin (RPR) test results in both serum and cerebrospinal fluid (CSF) samples from a patient undergoing treatment for neurosyphilis. Syphilis treatment is based on the rapid plasma reagin (RPR) and syphilis treponema antibody levels, and in the case of RPR-positive syphilis, a 1/4 reduction in the RPR value by the manual card test is considered curative. However, it should be noted that when RPR is followed by the manual card test, there may seem to be no reduction when the automated method shows a steady reduction. In the present case, initially under surveillance for an unrelated condition, was found to have symptoms; imaging and serological findings suggestive of syphilis infection including syphilitic aortitis and neurosyphilis. After two weeks of high-dose intravenous Penicillin G, the patient was treated with oral amoxicillin as an indicator of RPR titers in both the serum and cerebrospinal fluid (CSF) by automated latex agglutination. RPR in serum automated latex agglutination decreased to 1/4 at 14 weeks and treatment was terminated, with a subsequent downward trend. The RPR using the manual card test was 1/2 at 14 weeks. If only the manual card method was used, the patient might require a longer treatment. In conclusion, the automated latex agglutination method for monitoring the treatment response may be useful, especially in patients with high RPR titers.