Lichen planopilaris and frontal fibrosing alopecia cannot be differentiated by histopathology

Background: Lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA) represent 2 entities that cause primary cicatricial alopecia. These entities are clinically different; nevertheless, the literature suggests that FFA represents a form of LPP. The main argument in support of this hypothesis is that previous studies comparing the histologic findings have not found obvious differences between these diseases. Methods: Our objective was to more critically compare and contrast 20 histologic findings of these diseases in a large number of patients in order to determine any significant histologic differences between LPP and FFA. Results: We found 3 parameters that were statistically different, namely the presence of terminal catagen-telogen hairs (50% FFA vs 23.5% LPP; P = .020); a severe perifollicular inflammatory infiltrate (29.4% LPP vs 4.6% FFA; P = .010) and a zone of concentric lamellar fibroplasia (85.3% LPP vs 63.6% FFA; P = .041). Conclusions: Although a few histologic features differ between FFA and LPP, we believe that these differences are too subtle or non-specific to distinguish between them with confidence. Therefore, clinical correlation is essential to establish the diagnosis.