Lupus erythematosus mimicking mycosis fungoides: CD123⁺ plasmacytoid dendritic cells as a useful diagnostic clue

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

“…The interfollicular epidermis was largely spared by the inflammatory process. No significant intrafollicular or dermal deposits of mucin were observed, inconsistent with folliculotropic mycosis fungoides (FMF) and cutaneous lupus erythematosus (CLE), respectively 9‐13 . IHC evaluation revealed a significant population of small CD8(+) lymphocytes among the CD3(+) cells, with generally preserved expression of pan‐T cell markers, supporting the reactive nature of the inflammatory process.…”

“…Multiple, clustered miliary cysts and larger infundibular cysts may occur in different settings [including LPFT, milia en plaque (MEP), CLE, and FMF, among the others (Table 1)] 10‐12 . MEP is a rare condition of unknown etiopathogenesis, whose clinical presentation is characterized by the presence of one or more plaques containing multiple grouped asymptomatic milia in a specific location 17,18 ; lesions may have a unilateral or bilateral distribution.…”

“…Our report is the first to describe the number and distribution of pDCs in LPFT lesions. pDCs are bone‐marrow‐derived cells that are typically absent in normal skin, but may be found in the inflammatory infiltrate associated with various skin neoplasms as well as inflammatory dermatoses, including CLE 8,12,13 ; pDCs are key players in the innate immune response, because of their ability to produce large quantities of type I interferons in response to stimulation of intracellular sensors. In CLE, solar‐radiation‐induced epidermal injury is thought to induce release of self‐antigens, thus triggering the pDCs‐mediated innate immune response 8 .…”

“…In CLE, solar‐radiation‐induced epidermal injury is thought to induce release of self‐antigens, thus triggering the pDCs‐mediated innate immune response 8 . The evaluation of number and distribution of pDCs (by means of IHC staining for pDCs‐specific antigens such as CD123 or BDCA‐2) is known to provide useful diagnostic information for the differential diagnosis between CLE and histological simulators, including LP 8,12,13,24 . TCF‐4 is an obligatory master regulator of pDCs, regulating cell fate decision between interferon‐producing pDCs and antigen‐presenting classical dendritic cells 25,26 ; a TCF‐4/CD123 dual‐color IHC stain was recently proved to have a sensitivity of 100% and a specificity of 99.8% in the diagnosis of the pDCs‐derived blastic plasmacytoid dendritic cell neoplasm 27 .…”

Diagnostic utility of plasmacytoid dendritic cells in dermatopathology

“…While different studies had some variation in the systems used to immunohistochemically evaluate the presence of plasmacytoid dendritic cells (mainly by using CD123 or blood-derived dendritic cell antigen-2) and/or their product type I interferon (using myxovirus resistance protein A), they generally had in common the evaluation of plasmacytoid dendritic cell content, clustering and distribution. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] For plasmacytoid dendritic cell content, semi-quantitative scoring systems that evaluate plasmacytoid dendritic cells as a percentage of the total mononuclear infiltrate were more commonly used than absolute plasmacytoid dendritic cell counts in most of the studies. 11,12,[15][16][17][33][34][35][36] Plasmacytoid dendritic cell clusters were defined differently among studies, varying from clusters of at least 5 touching plasmacytoid dendritic cells, 23 ≥10 plasmacytoid dendritic cells, [15][16][17]25,26,30 ≥15 touching CD123 + plasmacytoid dendritic cells 28 to 20 or more cells.…”