Histopathologic and dermoscopic features of 42 cases of folliculitis decalvans: a case series

Abstract Background Folliculitis decalvans (FD) is a form of inflamed primary cicatricial alopecia (PCA). FD is classified as a neutrophilic PCA; however, only a few previous studies have described its histopathology, including the assessment of systematically evaluated and quantified follicular changes in horizontally sectioned biopsy specimens with clinical and dermoscopic findings of the early and advanced stages. Objective We aimed to clarify the histopathological and dermoscopic features of early and advanced active stage FD. Methods We conducted a case series study of 42 patients with FD by dermoscopy and both horizontally and vertically sectioned biopsy specimens. Results The histopathological findings of the early-stage lesions included loss of sebaceous glands, interfollicular acanthosis, and fibrosis with depressed, fused follicular infundibula showing thickened interfollicular keloid-like areas with tufted hairs on dermoscopy. Active lesions revealed a greater number of hair clusters, clefting, and fused infundibula with dense inflammation predominantly in the upper follicles. Neutrophil-predominant infiltrates were observed in less than half the patients, including those with early-stage lesions. Limitations This was a retrospective study. Conclusion FD has the features of mixed cell-PCA. The features of early-stage FD are thickened interfollicular keloid-like areas with tufted hairs and loss of sebaceous glands.