The presence of clusters of plasmacytoid dendritic cells is a helpful feature for differentiating lupus panniculitis from subcutaneous panniculitis‐like T‐cell lymphoma

Abstract

Both lupus panniculitis (LP) and subcutaneous panniculitis-like T-cell lymphoma (SPTCL) are characterized by subcutaneous lobular lymphocytic infiltrates, and they are sometimes difficult to differentiate. Recently, plasmacytoid dendritic cells (PDCs) were found to be present in various types of cutaneous lupus erythematosus lesions, including LP, and are supposed to play important pathogenetic roles. The aim of this study was to investigate whether PDCs are differentially present in these two diseases and can be utilized to differentiate them. Conventional histopathological features were also compared. Initial biopsies from 21 LP and 11 SPTCL patients were analysed. Our results showed that the presence of lymphoid follicles, dermal mucin deposition and lack of moderate to marked nuclear atypia or adipocyte rimming were more suggestive of LP. Several distinct patterns of fat necrosis, i.e. hyaline/lipomembranous and fibrinoid/coagulative in LP and SPTCL, respectively, were also diagnostically useful. Also, clusters of PDCs were characteristically seen in LP lesions (17/21, 81%) but not in SPTCL lesions (2/11, 18.2%). In LP lesions, but not in SPTCL lesions, the presence of epidermal interface change correlated perfectly with the presence of PDCs in the papillary dermis. We conclude that the presence of clusters of PDCs and certain histological features are helpful for the differential diagnosis.