Possible role of the bulge region in the pathogenesis of inflammatory scarring alopecia: lichen planopilaris as the prototype.
BACKGROUND
Lichen planopilaris (LPP) is the prototype of scarring alopecias that mainly target the infundibuloisthmic (bulge) region of hair follicle. Hair follicle stem cells have been shown to reside in the bulge.


METHODS
We carried out this study to better define the possible pathogenetic role of the bulge in LPP. Thirty-five cases of LPP were studied. Multiple serial sections of biopsy specimens stained with hematoxylin and eosin, periodic acid Schiff-diastase, and Elastic van Gieson. The following immunostains were applied: CD3, CD4, CD8, CD1a, and Ki-67. Uninvolved follicles and normal scalp biopsy specimens served as normal controls.


RESULTS
All cases showed a lichenoid lymphocytic infiltrate at the bulge region. The bulb area was spared. CD8(+) T cells were increased compared with CD4(+) T-cell population. Langerhans' cells were decreased. Proliferating stem cells, highlighted by Ki-67, showed a marked decrease in the bulge compared with uninvolved follicles.


CONCLUSIONS
Our study supports the finding that in LPP, the inflammatory infiltrate mainly involves the bulge region, where the stem cells reside. Once this area is damaged, the hair loses its potential of regrowth with resulting scarring alopecia. This is in contrast with inflammatory non-scarring alopecias such as alopecia areata, where the bulb region is targeted, sparing the stem cells.
Mobini
Narciss
N
Department of Dermatology, Section of Dermatopathology, New York University Medical Center, Suite 7J, 530 First Avenue, New York, NY 10016, USA.
Tam
Sam
S
Kamino
Hideko
H
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000505:Alopecia / Q000209:etiology / Q000276:immunology / Q000473:pathology*; D015703:Antigens, CD / Q000032:analysis; D002921:Cicatrix / Q000209:etiology* / Q000276:immunology / Q000473:pathology; D005260:Female; D018859:Hair Follicle / Q000276:immunology / Q000473:pathology*; D000949:Histocompatibility Antigens Class II / Q000032:analysis; D006801:Humans; D007150:Immunohistochemistry; D007249:Inflammation / Q000209:etiology / Q000473:pathology; D019394:Ki-67 Antigen / Q000032:analysis; D007801:Langerhans Cells / Q000276:immunology / Q000473:pathology / Q000502:physiology; D008010:Lichen Planus / Q000276:immunology / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D013234:Stem Cells / Q000276:immunology / Q000473:pathology; D013601:T-Lymphocytes / Q000276:immunology / Q000473:pathology
D015703:Antigens, CD; D000949:Histocompatibility Antigens Class II; D019394:Ki-67 Antigen