Serum RPR Testing Predicts Success of Neurosyphilis Treatment

New research finds that measuring the serum level of rapid plasma reagin (RPR) can generally predict the success of treatment for neurosyphilis, thereby avoiding lumbar puncture for confirmatory cerebrospinal fluid (CSF) testing.

Successful treatment for neurosyphilis is usually defined as normalization of CSF and clinical abnormalities. In the current study, researchers from the University of Washington-Seattle assessed whether normalization of serum RPR titers correlated with these outcomes. The team assessed these parameters in 110 neurosyphilis patients after four, seven and 13 months of treatment.

Serum RPR titer normalization occurred in 57 percent of patients by four months, 85 percent by seven months, and 88 percent by 13 months. Except for CSF protein levels, serum RPR titer normalization correlated with CSF and clinical abnormality normalization in more than 80 percent of patients at four months, more than 85 percent at seven months, and more than 90 percent at 13 months.

RPR titer normalization increased the odds of CSF and clinical abnormality normalization by up to 57-fold, the researchers reported. There was a caveat, however. "Normalization of serum RPR titer was consistently less accurate in predicting treatment success in [HIV-positive] patients who were not receiving antiretroviral therapy, compared with those who were receiving such therapy," the authors wrote.

"In most instances, normalization of serum RPR titer correctly predicts success of treatment of neurosyphilis, and follow-up lumbar puncture can be avoided," the authors concluded.

In an editorial, Dr. Daniel M. Musher speculated it is possible that some of the study patients did not actually have neurosyphilis. Even so, he agreed that serum RPR titer normalization "is a reliable predictor of a cure after treatment of neurosyphilis."

The report, "Normalization of Serum Rapid Plasma Reagin Titer Predicts Normalization of Cerebrospinal Fluid and Clinical Abnormalities After Treatment of Neurosyphilis," and the editorial, "Neurosyphilis: Diagnosis and Response to Treatment," were published in Clinical Infectious Diseases (2008;47(7):893-899 and 900-902).