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

Background: Histopathologic differentiation of lichen planopilaris (LPP) and discoid lupus erythematosus (DLE) as two common causes of primary cicatricial alopecias remains challenging.

Method: 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.

Result: 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.

Conclusion: The mast cell count detected by Giemsa staining could assist pathologists in distinguishing between LPP and DLE.