Immunohistochemistry profile of inflammatory cells in lichen planopilaris and discoid lupus erythematosus

Background: Scarring (cicatricial) alopecia represents a complex group of inflammatory disorders, mainly characterized by destruction of the hair follicle unit. Lichen planopilaris (LPP) and discoid lupus erythematosus (DLE) are the two main causes of primary cicatricial alopecia (PCA), both leading to hair follicle destruction and irreversible alopecia. However, they are different in pathogenesis and sometimes are diagnostically challenging. Methods: Twenty-eight formalin-fixed paraffin-embedded (FFPE) specimens of skin biopsies from 17 patients with a clinicopathologic diagnosis of LPP and 11 patients diagnosed as DLE were included. Histopathological study was performed with Haematoxylin and Eosin (H&E)-stained slides; then, immunohistochemical staining (IHC) was performed against CD20, CD3, CD4, and CD8 to evaluate and compare the type and distribution pattern of dermal inflammatory infiltrate. Results: Immunohistochemical findings showed a predominance of T-cells in both groups. CD8+ T-cells were significantly more abundant in LPP (15 cases with 10-50% of infiltration) than DLE (11 cases with <25% of infiltration) with preferential involvement of the perifollicular region (P <0.05). The proportion of CD4+ T-cells in DLE cases was significantly higher than LPP cases (9 cases with 10-50% of infiltration versus 15 cases with 0-10% of infiltration, respectively) (P <0.05) with perivascular and perifollicular distribution. Conclusions: This study supports the usefulness of IHC for CD4 and CD8 in the differential diagnosis of LPP and DLE in problematic cases.