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A girl in her teens presented for evaluation of asymptomatic, punctate, keratotic papules localized to the right palm and right third proximal finger that had been present since age 2 years. Prior treatments included cryotherapy, pulsed dye laser, and 40% salicylic acid, with partial improvement reported but never complete clearance. Medical history and family history were unremarkable. Physical examination revealed grouped and circumscribed, firm, skin-colored, 1- to 3-mm papules with a central punctate dark core (Figure, A and B). A 4-mm punch biopsy from a papule on the palm was performed (Figure, C and D).
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D. Nevus comedonicus
Punch biopsy results revealed dilated cystic spaces with mild squamous hyperplasia and central laminated keratin resembling a dilated terminal hair follicle infundibulum (Figure, C and D). The clinical and pathologic findings were considered diagnostic of a nevus comedonicus.
Nevus comedonicus is a hamartomatous proliferation resulting from improper keratinization of the pilosebaceous unit, and it presents as punctate papules with a central keratotic core. Individual lesions may be present at birth or develop during childhood, but they are generally fully established by age 10 years.1 Linear or blaschkoid presentations involving the face, neck, upper extremities, and trunk are most common, with a prevalence of 1 in 45 000 to 1 in 100 000 persons.2 However, palmar-plantar presentations have been described despite these areas being devoid of pilosebaceous units.3,4 Nevus comedonicus development is postulated to reflect abnormal filaggrin expression or overstimulation of fibroblast growth factor receptor 2, with high expression of interleukin 1 leading to improper pilosebaceous unit development.2 However, there is still debate as to whether development of nevus comedonicus, particularly on the palms and soles where pilosebaceous units are absent, may be caused by abnormal epidermal invagination. Histopathology is characterized by keratin-filled, dilated, cystic spaces with infundibular differentiation in the absence of hair shafts, arrector pili muscle, or sebaceous glands with variable acanthosis.2
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Corresponding Author: Megan Brinkworth Vissing, MD, Department of Dermatology, Mayo Clinic Florida, 4500 San Pablo Rd S, Jacksonville, FL 32224 (firstname.lastname@example.org).
Published Online: October 2, 2019. doi:10.1001/jamadermatol.2019.2956
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
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