Evaluation of the Diagnostic Value of Plasmacytoid Dendritic Cells in Differentiating the Lymphocytic Cicatricial Alopecias.

Background: Differentiating lymphocytic scarring alopecias may be difficult clinically as well as histopathologically.

Objective: To investigate plasmacytoid dendritic cell (PDC) presence and distribution patterns and their diagnostic value in differentiating scarring alopecias of lupus erythematosus (LE) from lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA).

Methods: Seventeen LE-associated alopecia, 20 LPP and 10 FFA cases were immunohistochemically tested for PDC presence/distribution and activity.

Results: LE-associated alopecia showed increased PDC content (≥10% PDCs in all cases and ≥50% in 94% of cases), PDC clusters (100% of cases), and deeper dermal and perieccrine distribution (100% of cases) with involvement of the dermoepidermal junction (DEJ, 94% of cases), while the majority of LPP and FFA had <10% PDC content that was mainly confined to the upper dermis surrounding the hair infundibulum with rare DEJ involvement and rare clustering.

Conclusions: Specific PDC-related parameters may serve as a useful diagnostic adjunct in the differentiation between LE-associated alopecia versus LPP and FFA.