Lichen planus follicularis tumidus: immunotyping of the inflammatory infiltrate with focus on plasmacytoid dendritic cells.

Lichen planus follicularis tumidus (LPFT) is a rare clinico-pathological variant of lichen planus (LP), clinically presenting with red-to-violaceous plaques studded with comedo-like lesions and keratin-filled milia-like cysts. Histopathologically, LPFT is characterized by cystically dilated follicular infundibula in the dermis, surrounded by a dense lichenoid lymphoid infiltrate with an associated interface reaction. We describe the clinico-pathological features of an additional case of LPFT, focusing on number and distribution of CD123(+) TCF4(+) plasmacytoid dendritic cells (pDCs). In our case pDCs represented approximately 5% of the total inflammatory infiltrate, predominantly exhibiting a lichenoid distribution around the infundibula with no evidence of cluster formation, thus ruling out cutaneous lupus erythematosus. Our report is the first to describe the number and distribution of pDCs in LPFT. The results of our immunohistochemical analysis corroborate the notion that LPFT should be regarded as a rare variant of LP. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.