Primary Syphilis of the Neck Mimicking Pyodermatitis

Diagnostic value of Treponema pallidum PCR test in real practice

BACKGROUND

Syphilis is a sexually transmitted infection (STI) caused by the pathogen Treponema pallidum. Its incidence is increasing in our country, especially among men who have sex with men (MSM). Serological tests are still the most widely used technique for diagnosis. The need for an early diagnosis has prompted the introduction of fast techniques, such as Treponema pallidum detection by polymerase chain reaction (PCR) on mucocutaneous samples. The objective of this work is to analyse the sensitivity of this technique in a series of patients diagnosed with syphilis at our centre.

METHODS

Retrospective review of all cases diagnosed with syphilis at our centre between May 2017 and May 2021.

RESULTS

A total of 203 cases of syphilis were diagnosed with serologic tests: 33% were primary syphilis and 53.1% secondary syphilis. PCR for Treponema pallidum was performed in 117 (57,6%) cases. The sensitivity was highest (95,2%) when performed on samples from mucocutaneous ulcers in primary syphilis. This value decreased to 69,4% in secondary syphilis, although there were variations between the types of samples.

CONCLUSIONS

The PCR test has a high diagnostic value when performed on ulcer exudates in patients with primary syphilis. Its most relevant advantages in clinical practice are the possibility of an early diagnosis before serological tests during the window period, the ability to confirm reinfections in patients with persistent positivity of reaginic antibodies and a history of treated syphilis. Nevertheless, given that a negative PCR test may not rule out infection by Treponema pallidum, serologic tests are still necessary for everyday practice.