Extension of separation along the follicular epithelium and follicular basement membrane in pemphigus and bullous pemphigoid

Background The outer root sheath of hair follicle and the interfollicular epidermis are continuous and basically similar in many aspects. The expression of various basement membrane (BM) components in the upper portion of the hair follicle is similar to that of the interfollicular BM. The extension of acantholysis into the adnexal structures was highlighted in the pemphigus group of diseases. On the other hand, extension of separation down the hair follicle BM has not been studied in subepidermal autoimmune bullous dermatoses. The aim of the present work was to study the extension of separation along follicular epithelium and follicular BM in pemphigus and bullous pemphigoid. Methods This retrospective study was conducted on pemphigus and bullous pemphigoid cases. For each case, 4‐μm‐thick sections stained with hematoxylin and eosin were examined for the presence of hair follicles and the extension of separation down follicular epithelium and follicular BM. Results Positive extension of acantholysis down the follicular epithelium was seen in 23/27 (85.2%) of pemphigus vulgaris (PV) and 7/9 (77.8%) of pemphigus foliaceus (PF) cases with hair follicles. Follicular extension was limited to the infundibulum in PF but down the entire follicular length in PV. As for bullous pemphigoid (BP) cases, 20/26 cases (76.9%) that had hair follicles showed positive extension of the separation down the follicular BM. The cellular infiltrate detected was identical in its nature and density to that of subepidermal blister in all cases. Conclusions Extension of the separation along follicular epithelium and follicular basement membrane was observed in PV, PF, and BP without significant difference.