Serologic tests for syphilis (STS) have been problematic for a multitude of reasons: lack of sensitivity in early darkfield positive cases, false positive results with common diseases and some tests remain serofast for life. In previous studies antitreponemal IgM has been observed in early syphilis and shown to rapidly decline post therapy. The aim of this study is to investigate IgM as a marker for syphilitic infection and to characterize its decline in response to treatment. The effects of HIV status, syphilis stage and history of syphilis infection on IgM response to treatment were examined. Patients and Methods: 44 patients with primary and secondary syphilis were retrospectively studied after treatment for seroreversion and 4-fold titer decline in the VDRL/RPR and 50% decline in antibody index (or negatively) in the Captia Symphilis-M test. Patients were followed for a maximum of 39 months post therapy between 1980 and 1985. Baseline information was collected regarding HIV status, syphilis stage and history of previous infection. Patients were asked to return to the clinic every 3-6 months for serologic testing. Results: The subjects had a mean age 32.2 years, 88.6% were male, 86.4% were Caucasian and 61.4% of patients reported homosexual or bisexual orientations. At baseline, 93.2% of the patients had detectable IgM compared with 97.7% reactivity in the VDRL/RPR test. Approximately 50% of patients responded to therapy by displaying a 50% decline in IgM. Nearly 100% of patients tested with the VDRL/RPR reached a 4-fold titer decline after treatment. Additionally, VDRL/RPR declined much more rapidly post treatment than Captia-M. HIV infection, syphilis stage and previous syphilis infection did not have a significant effect on response to treatment (4-fold decline in VDRL/RPR titer or 50% reduction in IgM antibody index). Seroreversion in Captia-M occurred in less than 60% of patients. Time to seroreversion was not affected by syphilis stage, HIV infection, or previous syphilis infection. Syphilis stage significantly affected seroreversion in the VDRL/RPR test. Patients with primary syphilis reverted faster than patients with secondary syphilis (p=.05). HIV and previous syphilis infection did not significantly affect VDRL/RPR seroreversion times. Conclusions: IgM was detected in 93.2% of all cases of early syphilis. Following therapy, IgM persists much longer than some previous studies have indicated, and HIV status, syphilis stage, and previous syphilis infection have no effect on seroreversion or antibody decline in the Captia-M test. Larger studies with extensive follow-up are needed to adequately assess IgM decline following treatment for early syphilis. These results suggest that titer decline in non-treponemal tests remains the most sensitive measure for monitoring treatment efficacy.
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