Hidradenitis suppurativa: a disease of follicular epithelium, rather than apocrine glands.

A retrospective study was made of the histopathology of axillary skin excised from 12 patients with hidradenitis suppurativa. In the majority of cases (10 out of 12), squamous epithelium-lined structures, in the form of cysts or sinuses were identified in the dermis. Laminated keratin was present in all these structures and half of the cysts also contained hair shafts, suggesting that they are derived from hair follicles. Only a small proportion of cases (4 out of 12) displayed inflammation in apocrine glands, and in these the inflammation was also seen around eccrine glands, hair follicles and the epithelium-lined structures. However, in cases where the epithelium of the 'cysts' was disrupted, the inflammatory infiltrate appeared to be centred around these areas. These observations suggest that the squamous epithelium-lined structures, which probably represent abnormal dilated hair follicles, are a more constant diagnostic feature in hidradenitis suppurativa than inflammation of apocrine glands which appears to be a secondary phenomenon.