This 42-year-old male developed numerous erythematous nodules and scaly papules over his lower extremities. He has chronic renal failure secondary to diabetes mellitus. This is a typical presentation for Kyrle disease (hyperkeratosis follicularis et parafollicularis in cutem penetrans), that is young to middle-age with diabetes and renal failure. Kylre disease is thought to represent an end-pathway for abnormal keratinization, possibly causing a "foreign-body-like" reaction to the patients own stratum corneum, but the etiology is largely unknown. This histology is also typical, in this case showing a parafollicular keratotic plug. A granulomatous reaction resides at the base of the keratin-filled channel. The differential diagnosis includes other perforating disorders, such as the perforating disorder of renal failure and/or diabetes, reactive perforating collagenosis, and perforating folliculitis. These entities show extreme overlap and may represent similar or the same processes, but can be distinguished by the location and the content of the channel.
Histologic sections of skin show a large keratotic plug, traversing the epidermis in a parafollicular location, with a slight epidermal invagination. The channel is filled with keratin, dense smudgy basophilic material, and inflammatory cells. At the base of the channel, there is a granulomatous inflammatory reaction. Irregular epidermal acanthosis is also noted.