Immunohistochemical distinction of lymphomatoid papulosis and pityriasis lichenoides et varioliformis acuta.

Lymphomatoid papulosis (LyP) and pityriasis lichenoides et varioliformis acuta (PLEVA) are benign self-healing cutaneous eruptions that may be clinically and histologically similar. However LyP has a 5% to 20% risk of associated lymphoid malignancy, whereas PLEVA does not. To determine whether the immunophenotype of lymphoid cells is useful in the distinction of these two disorders, the pattern of expression of lymphoid cell lineage and activation antigens in nine cases of LyP and seven cases of PLEVA were compared. In all cases of LyP most larger cells expressed the activation antigen Ki-1 (CD30) and lacked expression of the T-cell antigen CD7 and at least one other T-cell antigen (CD2, CD3, CD5). In contrast, CD30-antigen expression was rare or absent in PLEVA, CD3- and CD7-antigen expression was found in all cases, and diminished expression of T-cell antigens (CD2 and CD5) was seen in only one case. Diffuse expression of HLA-DR antigen by epidermal keratinocytes was found in a greater proportion of PLEVA cases (6 of 7) than LyP cases (3 of 6). In addition, CD8+ cells predominated at the dermal/epidermal junction in 3 of 6 cases of PLEVA but in only 1 of 7 cases of LyP. We conclude that LyP and PLEVA can be distinguished immunohistochemically in most, if not all, cases. Furthermore these results suggest that LyP and PLEVA are separate disorders, thus accounting for their variable prognoses.