Involvement of the bulge region in primary scarring alopecia.

While the pathogenesis of most scarring alopecias is poorly understood, one recent study indicates destruction of follicular stem cells as a possible mechanism in lichen planopilaris, the prototypic scarring alopecia. The aim of this cross-sectional study was to ascertain the target of inflammation and to more precisely characterize the inflammatory infiltrate in various stages of primary scarring alopecias. Immunohistochemical studies were performed using a panel of antibodies that included anti-cytokeratin 15, an antibody that specifically targets follicular bulge stem cells and CD4, CD8, CD1a and human leukocyte antigen-DR to characterize the inflammatory infiltrate. Our data showing absence of follicular bulge stem cells in cases with moderate to heavy inflammation suggest involvement of the bulge region in 'early' active stages of primary scarring alopecia. The paucity of CD8+ T cells in the inflammatory infiltrate in the majority of these cases argues against a cell-mediated cytotoxic destruction of follicular bulge stem cells. Preservation of CK15+ cells in 'late' fibrotic stages of primary scarring alopecia further supports this and implies that the irreversible loss of hair follicles, the sine qua non of primary scarring alopecia, is not necessarily a consequence of T cell-mediated destruction of follicular bulge stem cells.