Hydroa vacciniform pathology

Hydroa vacciniforme is a rare photodermatosis that usually presents in childhood as vesicles that heal with scars. Although he Pathogenesis is not well understood, Epstein Barr virus (EBV) can be detected in the dermal infiltrate. It is currently unclear whether hydroa vacciniforme T cell lymphoma is a discreet entity or is at the severe end of the hydroa vacciniforme spectrum.

Histology of hydroa vacciniforme

In hydroa vacciniforme, the sections show epidermal spongiosis, vesiculation and necrosis superimposed on a dense dermal infiltrate (figure 1). Necrosis can be confluent (figures 2, 3) and infiltrated by a mixture of acute and chronic inflammatory cells. In older injuries there may be scarring.

Figure 4 shows the denser infiltrate seen in hydroa vacciniforme-type T-cell lymphoma, which may have identical epidermal/superficial changes.

Special studies for hydroa vacciniforme

EBV can be detected in the dermal infiltrate (with in the place hybridization for EBER).

Differential diagnosis of hydroa vacciniforme

Vacciniform hydroa T-cell lymphoma: It is currently unclear whether this is a discrete entity or whether it falls within the vacciniform hydroa spectrum. With this lymphoma, the lesions are usually larger, do not resolve, and may also involve sites not exposed to the sun. The infiltrator in the dermis may be denser than seen in hydroa vacciniforme and the subcutaneous fat can be infiltrated (figure 4). Immunohistochemical studies reveal that the infiltrate is composed of CD3+. CD8+, TIA+ T cells or CD56+ NK cells. Gene Rearrangement studies may be positive. EBV in situ hybridization may be positive in the infiltrate.