Diagnostic Value of Plasmacytoid Dendritic Cells in Differentiating Pityriasis Lichenoides et Varioliformis Acuta From Lymphomatoid Papulosis.

Pityriasis lichenoides et varioliformis acuta (PLEVA) and lymphomatoid papulosis (LyP) can often demonstrate clinical and histopathologic overlap. A recent study demonstrated significant plasmacytoid dendritic cell (pDC) recruitment in lesions of PLEVA, whereas another study reported minimal pDC recruitment in lesions of LyP. To confirm the possible diagnostic value of pDCs in differentiating PLEVA and LyP, we compared the presence and distribution of pDCs and myxovirus protein A (MxA) expression (an indirect assessment of pDC activity). In total, 19 cases of PLEVA (16 patients) and 14 cases of LyP (11 patients) were examined using immunohistochemical stains for anti-blood-derived dendritic cell antigen-2 and MxA. Individual semiquantitative scoring systems were used to assess the immunohistochemical results, and a Mann-Whitney test with a subsequent 2-tailed P test was performed for statistical analysis. No statistically significant difference in the number of pDCs in both groups was found. However, most PLEVA cases (84%) demonstrated intense and diffuse MxA expression, whereas LyP cases (71%) demonstrated weak patchy staining (P < 0.007). Our study suggests that although additional studies may be needed to determine whether pDCs are more relevant to the pathogenesis of PLEVA or LyP, pDC activity through MxA staining may play a role in differentiating PLEVA from LyP and may serve as a platform for additional studies.