"Sexually Transmitted Infections" — Practice

Question 1

A single painless indurated genital ulcer with a clean base and non-tender rubbery bilateral inguinal nodes indicates

Accepted Answer

B

Question 2

Which test is used to monitor response to treatment in syphilis?

Accepted Answer

C

Question 3

A patient with clinically convincing secondary syphilis has a non-reactive VDRL. What has happened and what should be done?

Accepted Answer

The prozone phenomenon. In secondary syphilis antibody titres are extremely high, and excess antibody prevents the lattice formation on which the flocculation test depends, so undiluted serum gives a falsely non-reactive result.

The remedy is to repeat the test on diluted serum, which restores the antigen-antibody ratio and reveals strong reactivity at higher dilutions. A treponemal test such as TPHA will also be positive.

The wider lesson is that this test fails precisely when the disease is most florid, which is the opposite of intuition, so a non-reactive VDRL in a patient with a palm and sole rash and generalised lymphadenopathy is never accepted at face value.

Question 4

A 26-year-old man has a single painless indurated ulcer and asks only for a cream. Outline complete management.

Accepted Answer

This is a primary syphilitic chancre. Confirm with dark-ground microscopy where available and with serology, remembering that non-treponemal tests may still be negative in very early primary disease, so repeat testing is required.

Treat with a single dose of benzathine penicillin, and warn him about the Jarisch-Herxheimer reaction.

Test for HIV and other sexually transmitted infections, since coinfection is common and any STI diagnosis is an indication to look for the rest. Notify and treat partners, since treating him alone guarantees reinfection.

Finally, explain that the ulcer would have healed by itself without treatment, which is precisely why untreated syphilis progresses silently, so a cream alone would have appeared to work while the disease continued.

Question 5

A woman has a thin grey vaginal discharge with a fishy odour, clue cells on microscopy and a vaginal pH of 5.0. What is the diagnosis and should her partner be treated?

Accepted Answer

Bacterial vaginosis. The combination of thin grey discharge, fishy odour with a positive whiff test, clue cells and a pH above 4.5 is diagnostic, and it represents a shift in vaginal flora away from lactobacilli rather than an infection acquired from a partner.

Her partner should not be treated, because partner treatment does not reduce recurrence in bacterial vaginosis. This distinguishes it from trichomoniasis, which is genuinely sexually transmitted, gives a frothy yellow-green discharge with a strawberry cervix, and does require partner treatment.

Candidiasis, the third cause of discharge, gives thick white curdy discharge with intense itch and a normal pH, and also does not require partner treatment.

Question 6

A pregnant woman with latent syphilis reports penicillin allergy. What is the correct management and why?

Accepted Answer

Desensitisation followed by benzathine penicillin. It is the only agent reliably shown to treat the fetus as well as the mother. Doxycycline is contraindicated in pregnancy, and erythromycin does not cross the placenta adequately to treat congenital infection, so neither is an acceptable substitute.

The allergy history should first be examined carefully, since many reported penicillin allergies are not genuine IgE-mediated reactions. If genuine, formal desensitisation is performed in a setting equipped to manage anaphylaxis, and penicillin is then given.

She should be warned about the Jarisch-Herxheimer reaction, which occurs within hours of the first dose from released treponemal antigens, is not allergic, and in pregnancy can provoke uterine contractions and fetal distress, so treatment is given where fetal monitoring is available. Treponemes cross the placenta at any stage of pregnancy, so treatment is not deferred.

Question 7

A 30-year-old woman has been treated syndromically for vaginal discharge three times in six months. What is going wrong?

Accepted Answer

Repeated syndromic treatment without resolution indicates that at least one of four supporting steps has been omitted, and the most likely is partner treatment. Reinfection from an untreated partner is the commonest reason for apparent failure.

The second possibility is that the syndrome is being mistreated. Vaginal discharge is a poor predictor of cervical infection, and the actual cause may be bacterial vaginosis, which is a flora shift, or candidiasis, neither of which responds to antibacterial cover aimed at gonorrhoea and chlamydia.

Third, recurrent candidiasis specifically should prompt testing for diabetes and HIV. Fourth, she needs HIV and syphilis serology, which should have accompanied the first episode.

The practical answer is that recurrent disease is an indication to move beyond syndromic management, obtaining microscopy, pH and specific testing, and to ensure the partner is treated.

Question 8

A young man asks for doxycycline to take after sexual exposures, having heard it prevents infections. How should you respond?

Accepted Answer

He is describing doxycycline post-exposure prophylaxis, which is a real intervention with genuine evidence. A 200 mg dose within 24 hours and no later than 72 hours after condomless sex substantially reduces bacterial sexually transmitted infections, with the strongest effects on chlamydia and syphilis.

Three qualifications matter. The effect on gonorrhoea is much weaker, so it does not cover the full range of risk. Current guidance recommends it for specific higher-incidence populations, particularly men who have sex with men and transgender women who have had a bacterial STI in the past year, rather than for the general population. And there is documented concern that widespread use selects for resistance, with reduced doxycycline effectiveness against gonorrhoea already observed after implementation in some settings.

The right response is neither refusal nor a prescription on request, but a risk assessment, discussion of condoms and HIV pre-exposure prophylaxis where relevant, testing for existing infection, and a considered judgement about whether he falls within the target group.

Question 9

A newborn has snuffles, a maculopapular rash on the palms and soles, hepatosplenomegaly, and does not move one arm. Explain the findings and what will happen if untreated.

Accepted Answer

This is early congenital syphilis. Snuffles is a persistent infectious nasal discharge from treponemal infection of the nasal mucosa, and the maculopapular rash involving palms and soles mirrors the distribution seen in acquired secondary syphilis. Hepatosplenomegaly reflects systemic dissemination.

The immobile arm is pseudoparalysis of Parrot, caused not by nerve injury but by osteochondritis at the metaphysis making movement so painful that the infant refuses to move the limb. Radiographs show the metaphyseal changes.

If untreated, survivors develop the late stigmata, which are permanent. The Hutchinson triad comprises interstitial keratitis, eighth nerve deafness and Hutchinson incisors, and it is accompanied by saddle nose from destruction of the nasal septum, frontal bossing and sabre tibia. Since treponemes cross the placenta at any stage of pregnancy, all of this is prevented by antenatal screening and a single course of maternal benzathine penicillin.

Practice — "Sexually Transmitted Infections"

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