What diagnostic tests should a patient with a skin patch and history of unprotected sex undergo?

Diagnostic Tests for a Patient with Skin Patch and History of Unprotected Sex

For a patient presenting with a skin patch and history of unprotected sex, comprehensive STI testing along with dermatological evaluation including patch testing should be performed to identify both infectious and allergic causes.

Initial Testing for Sexually Transmitted Infections

Genital Lesion Testing

1. Nucleic Acid Amplification Testing (NAAT)

   • For HSV-1 and HSV-2 from lesion scraping or aspirate 1
   • For syphilis (if available) from lesion base

2. Direct Visualization Tests

   • Darkfield microscopy for Treponema pallidum (if available) 1
   • Direct fluorescent antibody (DFA) testing for HSV from lesion base 1

3. Serological Testing

   • Syphilis testing using both:
     • Nontreponemal test (VDRL or RPR)
     • Treponemal test (EIA/CIA, TPPA, or FTA-ABS) 1
   • HIV testing (essential component of genital lesion workup) 1

Additional STI Testing

• Chlamydia and gonorrhea NAAT from appropriate sites (urethral, cervical, rectal, pharyngeal)
• For women: HPV testing if age-appropriate (not recommended for patients ≤21 years) 1

Dermatological Evaluation

Patch Testing

• Indication: For patients with chronic or persistent dermatitis that could be allergic contact dermatitis 1
• Timing: Should be deferred for:
  • 6 weeks after UV exposure
  • 3 months after systemic agents
  • 6 months after biological agents 1

Patch Testing Procedure

1. Preparation:

   • Counsel patient about keeping the back dry during testing
   • Obtain informed consent 1
   • Select appropriate allergens based on history and exposure 1

2. Application:

   • Apply standardized concentrations of allergens to the skin under occlusion
   • Typically applied to the back using Finn chambers 1

3. Reading Schedule:

   • Optimal timing: Day 2 and Day 4
   • Consider additional reading at Day 7 to capture 10% more positive reactions 1

Special Considerations

For Suspected Seminal Plasma Allergy

• If history suggests reactions during or after intercourse:
  • Skin prick testing to whole seminal fluid 1
  • Consider specialized testing with seminal plasma protein fractions if initial test negative but suspicion remains high 1

For Suspected Food or Drug Allergies

• Consider atopy patch testing if history suggests reactions to specific exposures 1
• Particularly useful for non-IgE mediated reactions 1

Diagnostic Algorithm

1. First Visit:

   • Perform STI panel (NAAT for HSV, syphilis serology, HIV)
   • Take samples from lesions for direct testing
   • Schedule patch testing if chronic/recurrent dermatitis is present

2. Follow-up Visit (3-7 days):

   • Review initial test results
   • Perform patch test readings
   • Determine relevance of any positive patch test reactions to patient's condition

Pitfalls and Caveats

• Patch testing has sensitivity and specificity between 70-80% 1
• False negatives can occur if testing is performed too soon after immunosuppressive treatment 1
• Single readings of patch tests (at only 48 or 72 hours) may miss delayed reactions 2
• Antihistamines do not need to be avoided before patch testing unless testing for urticaria 1
• For syphilis, using only one type of test (treponemal or nontreponemal) is insufficient; both are required 1

Proper diagnosis requires correlation of test results with clinical presentation, as neither STI testing nor patch testing alone may identify the cause of the skin patch in the context of unprotected sex.