Perforating Folliculitis

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Background
Perforating disorders are characterized by transepidermal elimination of altered keratin or dermal connective tissue material. These disorders include perforating folliculitis (as shown below), Kyrle disease, elastosis perforans serpiginosa, reactive perforating collagenosis, and acquired perforating dermatosis. Cases of overlap are described, and diagnostic criteria are not well-defined for all the entities.[1] Clinically, the lesions are hyperkeratotic to verrucous papules and nodules.

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Typical appearance of lesions of perforating folliculitis consisting of keratotic follicular papules. In perforating folliculitis, keratotic follicular papules develop, particularly over extensor surfaces. Microscopically, the disorder is characterized by disruption of the infundibular portion of the follicular wall, with transepidermal (transfollicular) elimination of connective-tissue elements and cellular debris.
Perforating folliculitis may present as an isolated finding, apparently unrelated to other disease states, but also can be associated with chronic renal failure and diabetes mellitus. Perforating folliculitis is closely related, if not identical, to the acquired perforating dermatosis that occurs with chronic renal disease. Kyrle disease (hyperkeratosis follicularis et parafollicularis in cutem penetrans) may simply represent an exaggerated form of perforating folliculitis. In addition, another disorder of transepidermal elimination, elastosis perforans serpiginosa, occasionally displays involvement of follicular units.
Pathophysiology
As in Kyrle disease, the concept of an extrinsic keratin plug penetrating the epidermis generally has been discredited. Abnormally premature keratinization at the expense of proliferation is a possible explanation, as proposed by Carter and Constantine and Tappeiner et al in Kyrle disease.[2, 3] A role for fibronectin has been postulated. In addition, a primary alteration of connective tissue or deposition of foreign material within the superficial dermis, with subsequent engulfment and elimination by proliferative follicular epithelium, also is conceivable as a mechanism. Such a response to experimental implantation of foreign material has been described.
In addition, evidence suggests a pathologic role for excessively coiled hairs. Mehregan first proposed that curled hairs within follicular canals may act as springs, penetrating the lateral follicular wall, thereby initiating the process of transepidermal elimination.[4] Support for this concept has been provided by an ultrastructural study of acquired perforating dermatosis that showed hair shaft fragments within transepidermal channels, even in patients in whom follicular involvement was not demonstrable on routine light microscopy. Factors that may promote coiling of hairs include follicular hyperkeratosis (occasional perforated follicles can be identified in keratosis pilaris) or contact dermatitis (eg, resulting from formaldehyde in clothing). Finally, trauma, such as scratching of pruritic skin, may well play a significant role in lesional development, possibly by setting in motion one or more of the pathologic events described above.[5]
Epidemiology
Frequency
United StatesIncidence of perforating folliculitis in the United States is not known precisely, although the disorder is not uncommon. In Detroit, Michigan, 50 cases were reported during a 2-year period in the early 1970s, although this observation was followed by a declining incidence of new cases.
InternationalInternational incidence of perforating folliculitis is not known.
Mortality/Morbidity
Perforating folliculitis Morbidity is associated with the cosmetic appearance of lesions and the pruritus that occasionally accompanies them. Although cutaneous disease is insignificant, substantial morbidity or mortality rates can be seen in association with the primary underlying diseases, such as diabetes mellitus or chronic renal failure.
Race
Although generally no ethnic predilection has been identified, 1 study found a higher incidence of Kyrle disease in chronic renal failure among African American individuals.
Sex
Perforating folliculitis occurs equally in males and females; no sex predilection has been reported.
Age
Perforating folliculitis is more common in the second through fourth decades of life.

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