Dermatology MCQ - Viral Infections - Inoculation herpes simplex

A medical student develops a painful, swollen finger with grouped vesicles on an erythematous base 5 days after performing a traumatic digital rectal examination on a patient without gloves. A Tzanck smear of vesicular fluid shows multinucleated giant cells. Which of the following is the most likely diagnosis and the site of viral latency following this infection?

A) Herpetic whitlow; latency in the trigeminal ganglion
B) Orf; no latency established
C) Cellulitis; no latency established
D) Herpetic whitlow; latency in the sacral dorsal root ganglia
E) Pyogenic granuloma; no latency established

Correct Answer: A) Herpetic whitlow; latency in the trigeminal ganglion

Explanation

This scenario describes inoculation herpes simplex, specifically herpetic whitlow.

Key Clinical Features of Herpetic Whitlow:

• Transmission: Direct inoculation of HSV-1 or HSV-2 through broken skin (e.g., abrasions, cuts). Common in healthcare workers (e.g., dentists, respiratory therapists) after exposure to oral or genital secretions without gloves.

• Presentation:

  • Painful, erythematous, swollen digit (typically the distal phalanx).

  • Grouped vesicles on an erythematous base, which may coalesce and form pustules or ulcers.

  • Often accompanied by tingling, burning, or pain before vesicle appearance.

• Tzanck Smear: Reveals multinucleated giant cells, supporting herpesvirus infection (HSV or VZV).

Virologic Pathogenesis:

• Latency: After primary infection, HSV establishes latency in the sensory ganglia.

  • For HSV-1 (common in oral infections and herpetic whitlow), latency occurs in the trigeminal ganglion.

  • For HSV-2 (common in genital infections), latency occurs in the sacral dorsal root ganglia.

• Reactivation: Reactivation from latency can cause recurrent lesions at the inoculation site.

Why Not the Other Options?

• (B) Orf: Caused by a parapoxvirus from sheep/goats, presents as a solitary nodule with a targetoid appearance, and does not establish latency.

• (C) Cellulitis: Bacterial infection (e.g., Staphylococcus) causing diffuse erythema, warmth, and pain, but not grouped vesicles. No latency.

• (D) Herpetic whitlow; latency in sacral dorsal root ganglia: Incorrect latency site. Sacral ganglia are typical for genital HSV-2 infections, not whitlow.

• (E) Pyogenic granuloma: A benign vascular tumor often triggered by trauma, presenting as a friable, bleeding nodule—not vesicular and unrelated to viral infection.

Management:

• Oral antivirals (e.g., acyclovir, valacyclovir) to reduce duration and severity.

• Topical antivirals (e.g., penciclovir) may be adjunctive.

• Avoid debridement or incision to prevent bacterial superinfection or viral dissemination.

• Pain control and wound care.

Prevention:

• Glove use during procedures involving contact with oral/genital secretions.

• Hand hygiene to reduce transmission risk.

Prognosis:
Self-limiting in 2–3 weeks, but recurrences may occur due to viral latency.