SummaryBackground Pilonidal sinus (PS) is considered to belong in the category of follicular occlusion diseases (acne triad).
Objectives The aim of our study was to elucidate the pathogenesis of PS by evaluating its cytokeratin (CK) expression.
Methods CK expression in nine cases of PS was studied immunohistochemically using six antikeratin antibodies.
Results Infundibular-like epithelium contained CK1, 10 and 14 similar to normal infundibulum, but it did not contain CK17. In non-infundibular-like epithelium, CK14, 16 and 17 were detected similar to that in normal outer root sheath. CK expression in PS was similar to that in hidradenitis suppurativa, suggesting that sinus epithelium may be fragile, hyperproliferative and undifferentiated.
Conclusions PS can be classified in the same entity as follicular occlusion diseases based on CK expression.