What is the approach to diagnose and treat herpes from an oral ulcer?

Diagnosis of Herpes from Oral Ulcers

Laboratory confirmation through viral testing of the ulcer is essential for accurate diagnosis of herpes simplex virus (HSV) infection from oral ulcers, as clinical diagnosis alone can lead to both false positive and false negative results. 1

Clinical Presentation

HSV oral ulcers typically present with:

• Initial vesicular eruptions that burst to form shallow ulcers or erosions
• Lesions that heal spontaneously without scarring in approximately 10 days
• Possible prolonged healing due to secondary bacterial infection or immunosuppression 1
• Pain and discomfort at the site of lesions 2

Diagnostic Approach

1. Sample Collection

For optimal diagnostic yield:

• Open vesicles with a sterile needle
• Collect vesicle content with a swab for:
  • Immunofluorescence staining (apply to microscope slide)
  • Viral culture or nucleic acid amplification tests (NAATs) using appropriate transport media 1

2. Laboratory Testing Methods

In order of preference:

1. Nucleic Acid Amplification Tests (NAATs) - highest sensitivity and specificity
2. Viral culture - gold standard but takes longer
3. Immunofluorescence staining - rapid but less sensitive 1

3. Differential Diagnosis

Consider other causes of oral ulcers:

• Other infectious agents (Treponema pallidum, Haemophilus ducreyi)
• Non-infectious causes:
  • Inflammatory bowel disease (Crohn disease)
  • Behcet syndrome
  • Fixed drug eruption
  • Fungal infections 1, 3

4. Special Considerations

• Any oral ulcer persisting beyond 2 weeks requires further investigation to rule out malignancy 3
• In immunocompromised patients, all oral ulcers should be cultured for HSV regardless of location 4
• HSV infections may involve any intraoral site in immunocompromised patients, not just keratinized tissue 4

Key Diagnostic Pitfalls to Avoid

1. Relying solely on clinical appearance - Laboratory confirmation is essential as clinical differentiation from other causes is difficult 1

2. Delayed sampling - Collect samples early in the course of the lesion, preferably from intact vesicles before they rupture 1

3. Improper sampling technique - Follow proper collection methods to ensure adequate viral material is obtained 1

4. Missing recurrent intraoral HSV - While herpes labialis (lip lesions) is more common, intraoral recurrent HSV can occur, especially in immunocompromised patients 4

5. Assuming fever must be present - Up to 43.3% of patients with oral HSV may be afebrile 4

6. Failing to test for HSV in atypical locations - HSV can affect non-keratinized intraoral sites, especially in immunocompromised patients 4

By following this diagnostic approach, clinicians can accurately identify HSV as the cause of oral ulcers and initiate appropriate treatment with antiviral medications such as valacyclovir, which is indicated for the treatment of cold sores (herpes labialis) at a dosage of 2 grams twice daily for 1 day taken 12 hours apart, initiated at the earliest symptom 5.