Folliculitis decalvans and lichen planopilaris phenotypic spectrum: a case series of biphasic clinical presentation and theories on pathogenesis

Summary We present a series of 13 patients with clinical and histological features of both folliculitis decalvans ( FD ) and lichen planopilaris ( LPP ), either concomitantly, or sequentially as the clinical phenotype changed over time. This biphasic presentation of FD ‐ LPP is not as uncommon as would be expected from the lack of description in the literature. We discuss current theories about the pathogenesis of both LPP and FD , and speculate how abnormal immune responses may either predispose to secondary bacterial infection or be influenced by dysbiosis of the skin/hair follicle microbiome, resulting in inflammation and permanent hair follicle damage.