How to judge whether syphilis is cured after treatment? These indicators tell you the answer

Author: Lou Jinli, researcher/professor at Beijing You'an Hospital, Capital Medical University

Reviewer: Wang Lixiang, Chief Physician, Third Medical Center, PLA General Hospital

The 10th Chairman of the Science Popularization Branch of the Chinese Medical Association

Syphilis is a chronic, systemic infectious disease caused by Treponema pallidum, which is mainly transmitted through sexual contact and can also be transmitted vertically from mother to child. According to the different transmission routes, it can be divided into acquired (acquired) syphilis and congenital (congenital) syphilis; according to the different courses of the disease, it can be divided into early syphilis and latent syphilis. Clinically, it is divided into four stages: primary syphilis, secondary syphilis, tertiary syphilis and latent syphilis, and the clinical manifestations of each stage are different. In order to better understand and deal with syphilis, the following will introduce in detail the laboratory testing, diagnosis, treatment and prevention of syphilis.

First, in terms of laboratory testing, the diagnosis of syphilis usually relies on nonspecific serological tests such as RPR (rapid plasma reagin test) or TRUST (toluidine red unheated serum reagin test) and specific serological tests such as TPPA (Treponema pallidum particle agglutination test). When RPR or TRUST is positive, but TPPA is negative, this indicates that there may be a biological false positive reaction, that is, caused by a nonspecific immune response (such as pregnancy, etc.); if RPR is negative and TPPA is positive, it indicates that the patient may have been infected with Treponema pallidum. Although it is not a current infection, specific antibodies can exist in the body for a long time or even be carried for life. If the syphilis-specific antibody is positive, but the titer of RPR or TRUST changes from positive to negative, this usually means that the patient has been infected with syphilis and has been cured after standardized antibiotic treatment. It is worth noting that the continued presence of syphilis-specific antibodies does not necessarily mean current infection (current infection), and a comprehensive judgment needs to be made in combination with contact history, typical clinical symptoms and other examination results.

Figure 1 Original copyright image, no permission to reprint

Regarding the diagnosis of early and late syphilis, laboratory blood tests cannot determine the stage of the disease alone. The early and late stages of syphilis are mainly divided according to the time of infection. Infections of less than two years are considered early syphilis, while those of more than two years are classified as late syphilis. Different stages are important in guiding the choice of treatment options. The treatment strategies for syphilis at different stages are different. For example, early syphilis can usually be treated with a single dose of penicillin, while late syphilis may require a longer course of treatment.

Figure 2 Original copyright image, no permission to reprint

During the treatment process, syphilis patients need regular checkups to monitor the effectiveness of treatment. Changes in RPR titers are one of the important indicators for evaluating efficacy. Changes in RPR titers before and after treatment can help doctors determine whether the treatment is effective. Generally speaking, if the RPR titer drops more than four times after a period of treatment, the treatment is considered effective. Ideally, as treatment progresses, the RPR titer should gradually decrease until it is undetectable, that is, it turns negative. In addition, even if the RPR titer turns negative, patients still need regular follow-up to ensure that the disease is thoroughly controlled.

Depending on the stage of syphilis, the doctor may recommend additional tests, such as cerebrospinal fluid examination. This is because Treponema pallidum sometimes invades the central nervous system and causes neurosyphilis. Positive specific IgM antibodies in the cerebrospinal fluid are the key basis for diagnosing neurosyphilis, because IgM antibodies cannot pass through the blood-brain barrier due to their large molecular weight, so their presence in the cerebrospinal fluid strongly suggests the possibility of local infection. In addition to cerebrospinal fluid examination, syphilis DNA testing is also an important auxiliary diagnostic method, especially when conditions permit. By detecting Treponema pallidum DNA in cerebrospinal fluid, the presence of pathogens can be directly proved, thereby improving the accuracy of diagnosis.

For pregnant women, syphilis infection is a problem that cannot be ignored because it can be transmitted to the fetus through the placenta, causing congenital syphilis. Therefore, pregnant women who are known to have syphilis or are at high risk should be screened regularly during pregnancy, including testing for specific antibodies and non-specific antibodies. If syphilis infection is confirmed, appropriate treatment should be given immediately to reduce the risk of fetal infection. Newborns should also receive corresponding examinations after birth, especially within 18 months of birth, to ensure that any potential infection is detected and treated in a timely manner.

Finally, it is worth noting that even elderly people with no history of adverse sexual activities may have a positive result for syphilis. This may be caused by a variety of reasons, including past infection, false positive reactions (cross-reaction of non-specific antibodies), or recent infection. Therefore, for a positive syphilis test result, the doctor needs to understand the patient's medical history in detail, including whether there has been unclean sexual behavior, whether there have been recent operations that may cause infection (such as tooth extraction, surgery, etc.), and other factors that may affect the test results. Through comprehensive analysis, doctors can make an accurate diagnosis and provide patients with personalized treatment recommendations.