Congenital syphilis and perinatal STIs — branching viva

Opening question

Examiner: Take me through this infant. What is the most likely diagnosis, and what is your frame for managing it? [3]

Candidate: The most likely diagnosis is early congenital syphilis. The combination of hepatosplenomegaly, a copper-coloured maculopapular rash on the palms and soles, generalised lymphadenopathy, and snuffles — the profuse blood-tinged nasal discharge teeming with spirochaetes — is classic, and the painful limb suggests osteochondritis with pseudoparalysis of Parrot. The maternal treatment gap, only ten days before delivery when four weeks is needed, confirms high risk. My frame is two-layered: confirm and treat this infant now, and run the public-health response to the maternal, partner and next-pregnancy risk. I would isolate for the infectious secretions, confirm with comparative serology, and start ten days of intravenous aqueous penicillin. [6]

Examiner: Why ten days of intravenous penicillin rather than a single benzathine dose? [6]

Candidate: Because the central nervous system must be penetrated to treat neurosyphilis, and benzathine penicillin does not achieve reliable CSF concentrations. A symptomatic infant — or one with confirmed disease — gets aqueous crystalline penicillin G intravenously for ten days. A single benzathine dose is reserved only for the fully asymptomatic, well-evaluated, low-risk infant whose mother was adequately treated and whose serology is reassuring. [6]