Painful Vulvar Lesions After a New Partnership

An adult presents with several painful vulvar ulcers and dysuria after a new sexual partnership. Vesicles are no longer intact and a recent syphilis blood test was negative soon after exposure. Appearance alone is unreliable, coinfection occurs, and testing windows and lesion age must shape interpretation.

Case focus#

The decision is which lesion and blood tests to obtain immediately, whether to begin empiric antiviral or syphilis treatment based on probability and follow-up, and how to evaluate noninfectious ulcer, trauma, inflammatory disease, and malignancy without coercive examination.

This analysis concentrates on calibration. It compares plausible explanations, asks which observations genuinely discriminate among them, and keeps the working diagnosis open to revision as new evidence arrives.

Problem representation#

The useful representation is not a label alone. It combines the tempo of the problem, the setting, the physiologic or functional threat, the evidence already available, and the important information that is still missing. For this painful vulvar lesions analysis, the working frame must remain broad enough to compare Genital herpes, Primary syphilis, Aphthous or reactive ulcer, Inflammatory dermatosis without allowing a familiar first impression to become an untested conclusion.

The setting materially changes the plan: A confidential sexual-health clinic with lesion PCR, syphilis and HIV testing, pregnancy testing, microscopy, trauma-informed examination, and partner services.. Available monitoring, access to consultation, travel time, record continuity, and the reliability of follow-through alter what counts as a safe next step. A plan that is reasonable in a continuously monitored environment may be unsafe when results return after discharge or urgent reassessment is difficult.

Immediate safety priorities#

• Urinary retention or severe pain: Inability to void, dehydration, or uncontrolled pain may require urgent support.
• Pregnancy or immune compromise: Dissemination and fetal implications lower the threshold for expert care.
• Systemic or neurologic disease: Fever, meningismus, radicular pain, weakness, or widespread lesions raises complicated infection.
• Persistent, indurated, or bleeding lesion: Nonhealing atypical ulcer requires biopsy for neoplasia or inflammatory disease.

These findings guide how quickly to stabilize, consult, and escalate care. They do not establish a diagnosis; the causal assessment continues alongside the immediate response.

Prioritized differential diagnosis#

Genital herpes#

What supports it. Painful grouped vesicles or ulcers, tender nodes, dysuria, and positive lesion NAAT support HSV.

What argues against it or keeps uncertainty open. A late dry lesion can yield a false negative.

Discriminating next step. Swab a fresh lesion and type the virus when possible.

Primary syphilis#

What supports it. Ulcer and exposure support syphilis even when pain is atypical or HSV coexists.

What argues against it or keeps uncertainty open. Serology obtained before antibodies develop cannot exclude primary syphilis and must be interpreted against exposure timing.

Discriminating next step. Use serology, lesion testing where available, and planned repeat by window.

Aphthous or reactive ulcer#

What supports it. Acute deep painful ulcers after systemic illness with negative STI evaluation support a nonsexually acquired ulcer.

What argues against it or keeps uncertainty open. Repeated grouped vesicles with positive HSV nucleic-acid testing favor herpes over a reactive nonsexually acquired ulcer.

Discriminating next step. Exclude infection and systemic inflammatory disease before labeling.

Inflammatory dermatosis#

What supports it. Erosive lichen planus, lichen sclerosus, Behçet disease, or Crohn disease can ulcerate.

What argues against it or keeps uncertainty open. A single acute episode with pathogen-confirmed infection and no other skin, oral, eye, bowel, or joint findings lowers inflammatory dermatosis probability.

Discriminating next step. Use full skin and mucosal examination and biopsy when persistent.

Trauma, drug reaction, or malignancy#

What supports it. Mechanical injury, fixed-drug timing, induration, or nonhealing lesion supports these causes.

What argues against it or keeps uncertainty open. Typical HSV morphology, positive lesion testing, and healing with antiviral therapy make trauma, drug reaction, or malignancy less likely.

Discriminating next step. Assess safety and medicines and biopsy suspicious lesions.

Keep the ranked differential open to revision. Consider probability, the consequences of delay, reversibility, and the burden of testing together. A dangerous alternative may need early exclusion even when it is not the most likely explanation.

Evidence-gathering strategy#

• Confidential sexual, symptom, medicine, and safety history. Timing, partners, barriers, prior episodes, pregnancy, trauma, systemic symptoms, and products define probability. Interpretation: The interval from exposure to lesions and testing determines whether repeat syphilis or other infection testing is required.
• Consent-based vulvar and full mucocutaneous examination. Morphology, nodes, discharge, oral, skin, and anal lesions reveal cause and complications. Interpretation: Induration, bleeding, extensive mucosal disease, unusual distribution, or nonhealing lesions widen the evaluation to inflammatory disease and malignancy.
• HSV lesion nucleic-acid testing. NAAT from an active lesion has higher sensitivity than culture. Interpretation: A negative old-lesion test does not exclude HSV.
• Syphilis serology with window-aware repeat. Treponemal and nontreponemal algorithms establish infection and baseline activity. Interpretation: Early negative testing needs a scheduled repeat when exposure is recent.
• HIV, pregnancy, and targeted STI testing. HIV, pregnancy, and exposure-directed STI results change antiviral or antibiotic selection, fetal considerations, partner services, and follow-up. Interpretation: Tests are selected with consent and exposure, not automatically disclosed to partners.

Choose tests that can change a decision. Interpret results in light of timing, pretest probability, measurement limitations, and recent treatment. A reassuring result may have been obtained too early or under conditions that limit its meaning.

Progressive course and interpretation#

HSV nucleic-acid testing from a fresh ulcer is positive while initial syphilis serology is negative. The clinician explains that the negative result may precede seroconversion and schedules repeat testing. Severe urinary pain is managed and pregnancy, HIV, partner, and recurrence needs are addressed.

Changes over time provide further evidence. Improvement after treatment can support a mechanism without proving it. If treatment does not help, reconsider the diagnosis, how and when it was delivered, adherence, and competing pathology. Explain conflicting findings rather than averaging them away.

Management reasoning#

• Treat likely first-episode herpes promptly. Antiviral benefit is greatest when started early and severe disease may need escalation.
• Treat syphilis by established stage when indicated. Select antiviral dose and duration according to first episode versus recurrence, pregnancy, immune status, renal function, allergy, and neurologic complications; escalate for disseminated or central nervous system disease.
• Control pain and preserve urination. Topical comfort, oral analgesia, hydration, and catheter support when necessary prevent complications.
• Address noninfectious causes. Dermatology, gynecology, rheumatology, or biopsy follows persistent or systemic disease.
• Provide prevention and partner pathways. Condom counseling, suppressive therapy, partner services, vaccines, and HIV prevention are individualized.

Match management to severity and uncertainty. Specify monitoring targets, foreseeable adverse effects, and when to stop or escalate care. Drug choice, doses, and procedures depend on verified individual factors, current local protocols, contraindications, and the responsible treating team. The focus here is the reasoning behind those decisions and their safeguards.

Communication and shared decisions#

Obtain consent step by step, offer a chaperone and self-collection where validated, use neutral sexual language, and explain that an STI result does not establish infidelity or timing. Discuss partner notification, suppressive options, and transmission risk without shame.

Explain what is known and uncertain, why the next step is recommended, the alternatives, and which changes require urgent reassessment. Use teach-back, qualified interpretation when needed, and accessible formats. Assign responsibility for pending results so the discussion leads to a safer plan.

Continuity and safety net#

• Seek urgent care for inability to urinate, severe headache or neck stiffness, weakness, widespread rash, pregnancy with systemic illness, or uncontrolled pain.
• Avoid sexual contact during active lesions and until the treatment and prevention plan is understood.
• Repeat syphilis or other tests at the specified window even if symptoms resolve.
• Return for any lesion that persists, hardens, bleeds, recurs frequently, or does not fit the initial diagnosis.

Confirm follow-through. Record who will receive each pending result, when reassessment should happen, what to do if contact fails, and which clinical or functional outcome will show whether the plan is working.

Equity and systems analysis#

Sexual violence, criminalization, gender identity, disability, and lack of confidential insurance can deter care. Ensure privacy from companions, ask about safety, use anatomically accurate preferred language, and connect to low-cost testing and treatment.

Consider how transportation, medication cost, work schedules, caregiving, health literacy, language, disability access, digital connectivity, and prior experiences of care affect the presentation and the feasibility of the plan. Addressing these constraints supports both accurate diagnosis and fair care.

Reasoning capabilities demonstrated#

• Evaluates painful vulvar ulcers by lesion age, morphology, exposure timing, dysuria, systemic findings, pregnancy, trauma, and recurrence rather than diagnosing an infection from appearance.
• Keeps HSV, early syphilis, coinfection, aphthous or inflammatory ulceration, trauma, and malignancy active while using stepwise consent for examination and sampling.
• Obtains nucleic-acid testing from the best available lesion and interprets negative or early syphilis serology within its window, scheduling the exact repeat test instead of falsely reassuring.
• Starts empiric antiviral or syphilis treatment when probability, timing, pregnancy, severity, and follow-up support it, while treating urinary pain and defining recurrence care.
• Uses neutral language to explain that results do not establish infidelity or timing and protects confidential, affordable care across violence risk, gender identity, disability, insurance, and criminalization concerns.

Key takeaways#

• Genital-ulcer appearance alone is unreliable and coinfection is possible.
• A negative early syphilis test may reflect the testing window, so follow-up must be scheduled.
• Trauma-informed consent and confidential prevention care are part of diagnostic quality.