A male patient who tested positive for syphilis and received a single intramuscular dose of Bicillin L‑A (benzathine penicillin G) 2.4 million units on [date] now presents with penile tearing and discharge; what are the likely causes and how should he be evaluated and managed?

Penile Tearing After Recent Syphilis Treatment: Evaluation and Management

This patient's penile tearing is most likely unrelated to his recent syphilis treatment and represents either a new sexually transmitted infection (particularly herpes simplex virus), traumatic injury, or reinfection with syphilis rather than treatment failure. 1

Understanding the Clinical Timeline

The timing here is critical for your differential diagnosis:

• Benzathine penicillin G 2.4 million units IM is the correct first-line treatment for primary and secondary syphilis and achieves therapeutic levels for 18-25 days. 1, 2
• Treatment failure manifests serologically, not with new lesions immediately after therapy. 3 True treatment failure is defined by failure of nontreponemal titers to decline fourfold within 6 months, not by new physical findings shortly after treatment. 1
• Jarisch-Herxheimer reaction occurs within 24 hours of treatment and presents with fever, headache, and myalgia—not penile tearing. 1

Most Likely Diagnoses to Consider

Primary Differential: New STI (Not Treatment Failure)

Herpes simplex virus (HSV) is the most common cause of painful genital ulceration and "tearing" in sexually active individuals and should be your first consideration. 4

• Obtain viral culture or PCR from the lesion base for HSV-1 and HSV-2
• Consider co-infection testing for gonorrhea, chlamydia, and HIV if not recently performed 3, 1
• All patients with syphilis should be tested for HIV if not done at initial diagnosis 1

Secondary Consideration: Reinfection with Syphilis

Reinfection is common, particularly among men who have sex with men (MSM) who comprised 32.7% of primary/secondary syphilis cases in 2023. 4

• Perform dark-field microscopy or PCR of lesion exudate if available to detect Treponema pallidum 4
• Obtain quantitative nontreponemal testing (RPR or VDRL) to compare with baseline titers 1
• A fourfold increase in titers compared to post-treatment levels indicates reinfection 3

Tertiary Consideration: Traumatic or Mechanical Injury

Non-infectious causes including vigorous sexual activity, masturbation, or dermatologic conditions (lichen sclerosus, fixed drug eruption) should be considered if infectious workup is negative.

Immediate Evaluation Steps

Perform the following assessments at this visit:

1. Visual inspection and documentation of lesion characteristics (painful vs painless, vesicular vs ulcerative, single vs multiple) 1
2. Quantitative RPR or VDRL to compare with pre-treatment and immediate post-treatment titers 1
3. HSV PCR or viral culture from lesion base 4
4. HIV testing if not performed at initial syphilis diagnosis 3, 1
5. Nucleic acid amplification testing (NAAT) for gonorrhea and chlamydia from lesion and urethra 4

When to Suspect Actual Treatment Failure

True treatment failure is a serologic diagnosis made at 6-12 months, not a clinical diagnosis made weeks after treatment. 3, 1

Treatment failure indicators include:

• Failure of nontreponemal titers to decline fourfold by 6 months after treatment for early syphilis 1
• Sustained fourfold increase in nontreponemal titers at any follow-up visit 1
• Persistent or recurring signs/symptoms with rising titers at 6-month follow-up 1

Management Algorithm Based on Findings

If HSV is Confirmed:

• Initiate valacyclovir 1 gram orally twice daily for 7-10 days for first episode
• Counsel about suppressive therapy if recurrent episodes occur

If Reinfection with Syphilis is Confirmed:

• Retreat with benzathine penicillin G 2.4 million units IM as a single dose for early syphilis 1
• Evaluate for HIV infection before retreatment 3, 1
• Perform CSF examination if reinfection is likely (rather than treatment failure) to exclude neurosyphilis 1
• Intensify partner notification and counseling about risk reduction 1

If Workup is Negative:

• Treat empirically for HSV given high prevalence and clinical presentation
• Arrange close follow-up in 1 week to reassess
• Continue scheduled serologic monitoring at 6 and 12 months post-treatment 1

Critical Follow-Up Requirements

All patients treated for syphilis require quantitative nontreponemal testing at 6 and 12 months regardless of interim symptoms. 1

• Do not switch between RPR and VDRL when monitoring response, as results cannot be directly compared 1
• A fourfold decline in titers within 6 months indicates successful treatment for early syphilis 5
• 15-25% of successfully treated patients remain "serofast" with persistent low titers (<1:8) that do not indicate treatment failure 1

Common Pitfalls to Avoid

• Do not assume new lesions represent treatment failure without serologic confirmation and appropriate time interval 3, 1
• Do not retreat for syphilis without documented serologic failure or confirmed reinfection 3
• Do not neglect HSV testing in patients presenting with painful genital lesions, even with recent syphilis diagnosis 4
• Do not forget HIV testing if not performed at initial syphilis diagnosis, as co-infection affects management 3, 1