The presence of mast cells in lichen planopilaris and discoid lupus erythematosus of the scalp: A quantitative study

Histopathologic differentiation of lichen planopilaris (LPP) and discoid lupus erythematosus (DLE) as two common causes of primary cicatricial alopecias remains challenging.We performed a histopathologic study on a case series of LPP and DLE specimens to investigate the number, distribution, and morphology of mast cells as indices for differentiation of these two entities. H&E investigation and Giemsa staining for the detection of mast cells was performed.A total of 74 cases comprising 50 cases of LPP and 24 cases of DLE were assessed. The mean mast cell count and percentage were significantly higher in LPP group (p < 0.001). Mean degranulated mast cell count and the mean intact mast cell count were also significantly higher in LPP patients (p < 0.001). Most of the specimens, 58 (78.4%), showed both perifollicular and perivascular distribution of mast cells without significant difference between two groups. The morphology of mast cells was predominantly round-oval in 85.5%, predominantly fusiform in 13.5% with more frequent fusiform morphology in DLE group.The mast cell count detected by Giemsa staining could assist pathologists in distinguishing between LPP and DLE.