Hydroa vacciniforme

Definition

It is a very rare photodermatosis of childhood with recurrent vesicles on sun-exposed skin that heal with pox-like (varioliform) scars. It is now classified as a cutaneous form within the spectrum of Epstein-Barr virus (EBV)-associated T/NK-cell lymphoproliferative disorders.

Classification

• Classic form: benign, onset in childhood, papulovesicles on sun-exposed skin, mostly resolving by early adult life.
• Severe (systemic) form, termed "HV-like lymphoproliferative disorder" in the 2017 WHO classification: recurrent papulovesicular eruptions also on sun-protected skin, sometimes with facial oedema, fever, lymphadenopathy, oculomucosal lesions, gastrointestinal involvement and hepatosplenomegaly; progression to systemic T-cell or NK-cell lymphoma is possible. It is reported predominantly in children from Asia and Latin America.

Occurrence & epidemiology

It mostly affects children aged 3 to 15 years. It is diagnosed more often in girls; in boys it tends to start later and run a longer course.

Aetiopathogenesis

The trigger is ultraviolet light, most often long-wavelength UVA. The condition is frequently associated with chronic EBV infection; in the classic form, EBV-infected γδ T cells are increased.

Clinical features

• Sun-exposed sites: face, ears, hands, lower legs.
• About 30 minutes to 2 hours after sun exposure, burning, itching or stinging, followed by tense papules and vesicles, sometimes with facial swelling.
• Progression to umbilicated papules with black necrotic crusts on a red base; healing with pale depressed scars.
• First episode usually in spring, recurrences through the summer.
• Occasionally keratoconjunctivitis, photophobia and photo-onycholysis.

Histology

Spongiosis, vesiculation and epidermal necrosis overlying a dense dermal infiltrate; scarring in older lesions. EBV can be detected in the dermal infiltrate by EBER in situ hybridisation.

Diagnosis

• Clinical suspicion from the typical history and distribution; skin biopsy with EBER in situ hybridisation.
• Determine the EBV status.
• Look for signs of the severe form: involvement of sun-protected skin, fever, lymphadenopathy, hepatosplenomegaly.

Differential diagnoses

• Porokeratosis
• Xeroderma pigmentosum (XP)
• Urticaria
• Actinic prurigo
• Phototoxic dermatitis
• Erythema dyschromicum perstans (ashy dermatosis)
• Lupus erythematosus

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References (selection)

1. DermNet: Hydroa vacciniforme
2. DermNet: Hydroa vacciniforme pathology
3. PubMed: Hydroa Vacciniforme and Hydroa Vacciniforme-Like Lymphoproliferative Disorder: A Spectrum of Disease Phenotypes Associated with Ultraviolet Irradiation and Chronic Epstein-Barr Virus Infection (PMID 33297336)
4. PubMed: Hydroa vacciniforme: a distinctive form of Epstein-Barr virus-associated T-cell lymphoproliferative disorders (PMID 30998212)

Cross-references