Lichen planopilaris and frontal fibrosing alopecia cannot be differentiated by histopathology

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.

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.

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).

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.