Hydroa Vacciniforme
Hydroa vacciniforme (HV) is a very rare light-sensitive skin disorder (photodermatosis) that usually begins in childhood, between the ages of 3 and 15. Sun-exposed skin develops vesicles and blisters with a central dip (umbilication), which crust over with blood and heal with permanent, pitted pox-like scars (varioliform scars).
For a long time the cause of HV was unknown. Modern molecular studies have since shown that it is fundamentally tied to chronic Epstein-Barr virus (EBV) infection of cytotoxic (CD8+) T cells or natural killer (NK) cells.
- Cytotoxic Injury Driven by EBV-Infected T/NK Cells:
- Ultraviolet light, especially UVA, acts as the local trigger. Sunlight increases the expression of cytokines and chemokines, which draw EBV-carrying CD8+ T cells or NK cells into the exposed skin.
- These infected immune cells release cytotoxic proteins (perforin and granzyme B) that directly kill epidermal keratinocytes and small dermal vessels, producing deep vesicles with central necrosis.
- The HV Spectrum, from Benign to Malignant:
- Classic hydroa vacciniforme: disease is confined to the skin, runs a chronic course and tends to fade as the patient reaches adulthood.
- HV-like lymphoproliferative disorder (HV-LPD): a more aggressive form in which EBV-infected T or NK cells undergo monoclonal expansion. It comes with systemic symptoms (persistent high fever, swollen lymph nodes, enlarged liver and spleen, low blood counts) and can transform into extranodal T/NK-cell lymphoma.
- Histopathology and Immunohistochemistry:
- Epidermis: marked reticular degeneration and necrosis, forming intraepidermal vesicles filled with necrotic keratinocytes and red blood cells.
- Dermis: a dense lymphocytic infiltrate around blood vessels and hair follicles, with some neutrophils present.
- EBER-ISH, the gold standard: in situ hybridization for EBV-encoded RNA (EBER) is clearly POSITIVE in the lymphocytes infiltrating the dermis.
Although HV is a light-induced skin disease, any child with umbilicated blisters that leave pox-like pitted scars must have a blood EBV DNA load measured by PCR and a skin biopsy stained with EBER-ISH. Telling classic hydroa vacciniforme apart from HV-like lymphoproliferative disorder (HV-LPD) can be a matter of life and death, because it determines the risk of malignant transformation.
Clinical Features and the Development of Varioliform Scarring
Flares are typical in spring and summer. Symptoms start anywhere from 1–2 hours to several hours after sun exposure.
- How the Skin Lesions Evolve:
- Early stage: stinging, itching or intense burning on sun-exposed skin (face, ears, neck, backs of the hands), followed by red, swollen papules.
- Blistering stage: within 24 hours the papules turn into tense vesicles and blisters containing clear or blood-stained fluid. The hallmark is a central umbilication, caused by necrosis of the epidermis.
- Crusting and scarring stage: the blisters break and form firmly adherent dark brown or hemorrhagic crusts. When the crusts fall off (after 1–2 weeks), they leave sharply defined, round or oval, whitish depressed scars resembling smallpox scars (varioliform or pox-like scars).
- Mutilating Complications:
- In severe or long-standing HV, repeated damage to the ears can destroy the cartilage, leading to contraction and partial loss of the outer ear (mutilation of the ear pinna).
- Eye involvement: conjunctivitis, iritis and corneal scarring that can impair vision (seen in 10–20% of cases).
- Systemic Warning Signs (Red Flags for HV-LPD):
- Persistent, unexplained fever after sun exposure.
- Generalized lymph node swelling, enlarged liver or spleen.
- Severe allergic-type reactions to mosquito bites (hypersensitivity to mosquito bites, HMB).
Diagnosis, EBV DNA Load Screening and Treatment at Haute-Derma
At Haute-Derma, patients with suspected hydroa vacciniforme are managed under our comprehensive EBV assessment and HV-LPD risk stratification pathway (Haute-Derma HV Protocol):
Gold-Standard Biopsy and Laboratory Workup
- Skin biopsy with EBER-ISH: we sample an intact necrotic vesicle within the first 24–48 hours and stain it with EBER-ISH to confirm EBV in the infiltrating lymphocytes.
- EBV DNA load by PCR: we quantify EBV DNA copies in peripheral blood mononuclear cells (PBMCs) and serum. A load above 10³ copies/mL strongly points toward systemic HV-LPD.
- T-cell receptor (TCR) gene rearrangement: assesses T-cell clonality to catch malignant transformation early.
Treatment of Classic HV
- Strict UV protection: a medical-grade broad-spectrum sunscreen with high UVA protection (UVA-PF > 30), combined with UPF 50+ sun-protective clothing.
- Systemic immunomodulators:
- Hydroxychloroquine: 4–6 mg/kg/day to dampen light-induced inflammation.
- Cyclosporine A: 3–5 mg/kg/day during severe flares to suppress activation of EBV-infected cytotoxic T cells.
- Low-level light therapy (LLLT, 630 nm): supports healing of necrotic wounds and reduces the risk of deep pitted scars.
Multidisciplinary Management of HV-LPD
- When HV-LPD is diagnosed together with a high EBV load or a monoclonal TCR rearrangement:
- We work closely with hematology–oncology.
- Systemic chemotherapy: regimens used for T/NK-cell lymphoma, such as SMILE (steroid, methotrexate, ifosfamide, L-asparaginase, etoposide).
- Allogeneic hematopoietic stem cell transplantation (HSCT): currently the only potentially curative option, and it improves survival in patients with systemic, progressive HV-LPD.
