Pityriasis lichenoides: A cytotoxic T-cell-mediated skin disorder. Evidence of human parvovirus B19 DNA in nine cases

BACKGROUND: Pityriasis lichenoides et varioliformis acuta (PLEVA) and pityriasis lichenoides chronica (PLC) probably represent the polar ends of the same pathologic process, i.e. pityriasis lichenoides (PL), with intermediate forms in between. Previous studies have demonstrated that the inflammatory infiltrate in PLEVA is composed of cytotoxic suppressor T cells, whereas in PLC the helper/inducer T-cell population drives the immunological answer. Furthermore, monoclonal rearrangement of the T-cell receptor-gamma (TCR-gamma) genes was repeatedly found both in PLEVA and PLC. METHODS: Forty-one formalin-fixed, paraffin-embedded tissue specimens of 40 cases of PL were retrieved from the files of the authors. Immunophenotyping for cytotoxic granular proteins (Tia-1/GMP-17 and Granzyme B) and T-cell-related antigens (n = 41), TCR-gamma chain gene analysis (n = 30) and molecular investigations for parvovirus B19 (PVB19) DNA (n = 30) were performed. RESULTS: Overlapping immunophenotypes were observed in PLEVA and PLC. The dermal and epidermal T cells predominantly expressed CD2, CD3, CD8, and Tia-1 with a variable positivity for CD45RA, CD45RO, and Granzyme B. A monoclonal rearrangement pattern of the TCR-gamma genes was detected in three cases (10%). PVB19 DNA was found in nine cases (30%). T-cell monoclonality in conjunction with genomic PVB19 DNA was present in one case. CONCLUSIONS: Our results demonstrate that PL is a skin disorder mediated by the effector cytotoxic T-cell population. The identification of PVB19 DNA in nine cases may be interpreted ambiguously: PVB19 as a true pathogen or as an innocent bystander.