Kyrle’s disease (hyperkeratosis follicularis et parafollicularis in cutem penetrans), sometimes classified as a disorder of keratinization, is one of the four conditions that are regarded as primary perforating disorders. Having said so, the nature/number of perforating disorders is uncertain. The epidermal involvement may be secondary to dermal disease and hence they are probably not true disorders of keratinization.
Kyrle’s disease lesions present as pruritic keratotic papules/nodules developing on the limbs and trunk. The plug protrudes from a crateriform depression from which it can be removed. In Flegel’s disease (hyperkeratosis lenticularis perstans), an autosomal dominant condition, there are also keratotic papules but they have polygonal margins (cornflake sign) and these differ from Kyrle’s disease lesions.
Many dermatoses occasionally exhibit the phenomenon of transepithelial elimination, in which material from the dermis is extruded through the epidermis to the exterior with little or no disruption of the surrounding structures. The extruded material may include inflammatory cells, red blood corpuscles, microorganisms and extracellular substances, such as mucin or altered connective tissue components. In most of these conditions, the elimination is secondary to some underlying disease (hence called secondary perforating disorders), such as perforating granuloma annulare where material in the centre of a palisaded granuloma seated immediately beneath the epidermis is deported from the skin. Occasionally, a chemical that has been applied to the skin topically or by intradermal injection can be eliminated by the transepidermal route to produce a perforating disorder.
There are four conditions that are regarded as primary perforating disorders: Kyrle’s disease, perforating folliculitis, reactive perforating collagenosis and perforating serpiginous elastosis (also called elastosis perforans serpiginosa). It is possible that these primary perforating disorders might be due to defects in the epidermal keratinocytes, hair follicle, collagen and elastic fibres, respectively, with the elimination being the final pathway but it should be noted that in perforating folliculitis, the follicular epithelium shows one or more perforations INTO the dermis. Moreover, perforating folliculitis might not vary sufficiently from any folliculitis in which the follicles have ruptured hence considered by many as non specific entity.
Perforating serpiginous elastosis is easily distinguished from other perforating disorders when characteristic serpiginous lesions are present (in contrast to individual papules in the latter) and by the finding of elastic fibres in the perforating tissue on histopathology but a similar histopathological appearance can occur in the acquired reactive perforating dermatosis (see below) .
These four conditions appear to be separate entities when they occur outside the setting of renal failure and/or diabetes mellitus. There have been numerous reports of these four perforating dermatoses occurring in the setting of renal failure and/or diabetes mellitus (largely on the basis of the histopathologic findings). The four conditions may overlap in such circumstances (e.g. both collagen and elastic fibres can be extruded in the same patient) and the name acquired reactive perforating dermatosis [perforating substances: Necrotic material – collagen – elastic tissue) has been suggested. It must be noted that Kyrle’s disease was first described in a young diabetic female and some actually consider Kyrle’s disease to be synonymous with acquired perforating dermatosis.
The late A Bernard Ackerman used to stress that the perforating concept is not a requisite for accurate morphologic diagnosis and does not illuminate the mechanisms that underlie those diseases. He actually considered Kyrle’s disease to be akin to suppurative folliculitis that induces intense pruritus. Intense pruritus leads in turn to prurigo nodularis superimposed on a resolving folliculitis.
Some add a fifth disease to the primary perforating disorders, that is perforating periumbilical calcific elastosis with its periumbilical keratotic papules (perforating substance is calcified elastic tissue), a grinding sound can be heard on performing a biopsy!
In most cases of acquired perforating dermatosis, lesions could be cleared by treatment with potent topical or intralesional steroids, some patients improve spontaneously though. Topical tretinoin may reduce the lesions.