Perianal comedones: a benign and rarely documented entity

Comedones form due to pilosebaceous ductal hyperkeratinisation.1 Proliferation of keratinocytes within the duct results in occlusion of sebaceous secretions and accumulation of an abnormally high amount of sebaceous lipids.1 Comedone formation is likely multifactorial.2 Postulated contributory factors include abnormal levels of lipids such as linoleate and squalene, the proinflammatory cytokine interleukin-1 alpha, leptin, vitamin A deficiency, bacteria and ingredients in skin care products such as cocoa butter and esters.1 Comedones are commonly reported in acne vulgaris, hidradenitis suppurativa, Favre-Racouchot syndrome, Apert syndrome and nevus comedonicus, and rarely reported in other conditions such as folliculotropic mycosis fungoides, Birt-Hogg-Dube syndrome and following occupational exposure to coal tar, oil and dioxin.1 2 While the distribution of comedones in these conditions is varied, none are associated with comedones occurring in the perianal region. According to the literature, there are only three previous case reports of perianal comedones. The earliest report inferred an association of perianal comedones with chronic topical fluorinated steroid application to the anus, which was prescribed for pruritus secondary to chronic diarrhoea.3 The authors suggested that topical steroids can render the follicular epithelium more responsive to the comedogenic effects of sebum in addition to having an occlusive effect.3 A letter in response to this report questioned the association of perianal comedones and topical steroids, supported by anecdotes of patients presenting with anal comedones associated with pruritus, without previous topical steroid use.4 In the latter two case reports, perianal comedones were asymptomatic incidental findings and not associated with use of topical steroids, as noted in our patient.1 2 The occlusive conditions of the perianal region together with the potential for this region to be more prone to irritant dermatitis are possible explanations for the development of comedones in this unusual location.1 The documented rarity of perianal comedones in the literature may be secondary to under-reporting both because of the potential for this entity to be asymptomatic and because of the infrequent examination of the perianal region as part of a complete skin examination.1 2 However, one would expect perianal comedones to be noted as an incidental finding by doctors who regularly perform endoscopies and rectal examinations.