DR10.2 | Syphilis Diagnosis — Summary & Reflection

KEY TAKEAWAYS

Diagnosing syphilis means reading the stage from clinical features and then choosing and interpreting the right test. Primary syphilis is the single, painless, indurated chancre with non-tender bilateral lymphadenopathy; secondary is the disseminated, highly infectious stage (palmoplantar rash, condyloma lata, mucous patches, generalised lymphadenopathy); latent is positive serology without signs (early <2 years vs late >2 years); tertiary is gummata, cardiovascular syphilis, and neurosyphilis; and congenital syphilis has early signs and late stigmata (Hutchinson's triad). Treponema pallidum is an uncultivable spirochaete that disseminates early and evades immunity, explaining the staged course. Diagnostically, dark-ground microscopy of a fresh chancre demonstrates the organism (not on oral lesions); non-treponemal tests (VDRL/RPR) screen and monitor by titre but suffer biological false positives; treponemal tests (TPHA/FTA-ABS/TPPA) confirm but remain reactive for life. A reactive non-treponemal with a negative treponemal test is a biological false positive, and the stage assigned drives the treatment chosen in the next SDL.

REFLECT

Return to the man in the opening scenario whose painless sore healed on its own. Why is it that the very feature that reassures the patient — painlessness — is the one that should most concern the clinician, and how will you make sure you never dismiss a painless genital ulcer? Now imagine you are screening a pregnant woman and her VDRL comes back reactive: before you alarm her, what is the one test you would order to decide whether this is true syphilis or a biological false positive of pregnancy, and how would you explain the wait to her? Thinking through these two situations — the missed chancre and the antenatal false positive — prepares you for the two ways syphilis serology most often catches clinicians out.