Multiple, comedo-like openings filled with keratin plugs

Nevus comedonicus is a rare hamartoma of the pilosebaceous unit. Nevus comedonicus is considered an epidermal nevi syndrome and is characterized by dilated comedo-like openings with black-brown keratin plugs following the lines of Blaschko.1-3 Nevus comedonicus occurs at an incidence...

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Nevus comedonicus is a rare hamartoma of the pilosebaceous unit. Nevus comedonicus is considered an epidermal nevi syndrome and is characterized by dilated comedo-like openings with black-brown keratin plugs following the lines of Blaschko.^1-3 Nevus comedonicus occurs at an incidence of 1/45,000 to 1/100,000; it typically appears at birth or early childhood and demonstrates accelerated growth during puberty.^1,2,4 Nevus comedonicus does not demonstrate preference for race or sex.⁴

Complications include inflammation or secondary infections, and bilateral and widespread nevus comedonicus is often associated with the neurocutaneous condition nevus comedonicus syndrome.^1,4-6 Patients with nevus comedonicus syndrome have central nervous system abnormalities, including epilepsy, electroencephalographic abnormalities, and transverse myelitis. They have skeletal abnormalities, including scoliosis, pectus excavatum, spina bifida occulta, syndactyly, and hemivertebrae. They may also have cutaneous abnormalities, including ichthyosis, leukoderma, and Sturge-Weber syndrome, and ocular abnormalities, including congenital cataracts, strabismus, and microphthalmus.^4,5 These extracutaneous manifestations usually manifest ipsilateral to the nevus comedonicus.⁶ Although malignant transformation of nevus comedonicus is very rare, it is often reported in association with benign epithelial tumors, including hidradenoma papilliferum, syringocystadenoma papilliferum, and keratoacanthomas.⁶

Nevus comedonicus manifests as closely arranged, dilated follicular ostia containing keratinous plugs resembling blackhead comedones that are typically grouped in a linear distribution along the lines of Blaschko.⁶ Although it is typically unilateral, it may be bilateral, and it can also be arranged in dermatomal, interrupted, or segmental patterns.⁴ Usually, nevus comedonicus is asymptomatic, without inflammatory acne lesions.⁶ Sebaceous glands are not normally found on the palms and soles, and involvement of these areas is rarely reported.⁴ Nevus comedonicus is categorized into two forms based on clinical appearance: a form with predominant comedones and a form in which the comedones undergo inflammatory changes with severe cutaneous sequelae.^2,4,7 In the comedone-predominant form, the nevus comedonicus merely represents a cosmetic defect with comedo-like changes.^2,4,7 In the other form, patients develop large follicular cysts, which tend to recur and form fistulas, abscesses, and keloids.^2,4

Nevus comedonicus is caused by growth deregulation of the mesodermal portion of the pilosebaceous unit, resulting in follicle-based hamartomas, which prevent the affected follicular structures from developing terminal hair and sebaceous glands.⁶ Instead, the hamartomas produce soft keratin or vellus hair, which occlude the adnexal ostia.⁶ Improper keratinization of the pilosebaceous unit is thought to occur through a number of different mechanisms including overstimulation of the fibroblast growth factor receptor 2 with high expression of the interleukin-1α, involvement of γ-secretase, and involvement of filaggrin.⁴

The differential diagnosis for nevus comedonicus includes segmental acne, which typically presents in puberty with polymorphous lesions and distinct histology showing sebaceous hyperplasia; trichofolliculoma, which presents in adults as a single nodule with a central pore draining sebaceous material; familial dyskeratotic comedones, which is an autosomal dominant condition presenting in puberty with widespread, symmetrically distributed comedo-like, hyperkeratotic papules; folliculocystic and collagen comedo hamartoma, which is an autosomal dominant condition presenting with large, painless, infiltrated plaques with numerous follicular comedo-like openings and cysts draining keratinous material; and Favre-Racouchot syndrome, which is a condition that typically affects middle-aged to elderly individuals and consists of multiple open and closed comedones in skin with actinic damage.⁷

Diagnosis of nevus comedonicus is clinical, but it can be confirmed with histopathology.² Nevus comedonicus also has classic dermoscopy findings, demonstrating numerous circular and barrel-shaped homogenous areas in light- and dark-brown shades with deep keratin plugs.² In contrast, acne vulgaris demonstrates numerous light or dark brown homogenous areas that are predominantly circular and are situated superficially.² Characteristic findings of nevus comedonicus on histopathology include large, grouped, dilated follicular ostia filled with keratin and devoid of hair shafts.¹ Singular rudimentary glands may be present at the bases of the follicular invaginations.⁷ Hyperkeratosis and acanthosis of the epidermis may be present, but para- or dyskeratosis are not present.⁶ Electron microscopy reveals more abundant tonofilaments in the upper part of the stratum spinosum and numerous keratohyalin granules.⁷ Increased numbers of Langerhans cells may also be present, whereas arrector pili muscles are absent or incompletely differentiated.⁷

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Treatment for nevus comedonicus is usually provided for cosmetic reasons; however, in severe cases, the goal is to alleviate inflammation. In general, the lesions do not spontaneously regress, but, given the benign nature of the condition, patients do not require aggressive therapy.⁶ Conservative options include emollients, topical corticosteroids for inflammatory lesions, keratolytic agents, and topical retinoids, which have limited efficacy as monotherapy, but can be combined with calcipotriol.⁶ In contrast, oral isotretinoin is typically ineffective.⁶ Complete surgical resection is the only definitive treatment, but defining the borders of the nevus comedonicus is difficult.⁶ Other treatments that have led to improvement include erbium:yttrium-aluminum garnet laser treatment and carbon dioxide ultrapulsed or diode lasers.^1,6 Cryosurgery, comedo extraction, and dermabrasion have had unsatisfactory results.⁶

In our case, the condition and treatment options were discussed with the patient. Because she desired complete resolution, she was treated with surgical removal of the lesion.

Melinda Liu, BA, is a medical student and Maura Holcomb, MD, is a dermatology resident at Baylor College of Medicine in Houston.

References

1. Bhullar A, Shamsudin N. Images in clinical medicine. Nevus comedonicus. N Engl J Med. 2015;372(26):2541.
2. Kamińska-Winciorek G, Spiewak R. Dermoscopy on nevus comedonicus: a case report and review of the literature. Postepy Dermatol Alergol. 2013;30(4):252-254.
3. Dessinioti C, Antoniou C, Katsambas A. Acneiform eruptions. Clin Dermatol. 2014;32(1):24-34.
4. Ganjoo S, Mohanan S, Kumari R, et al. Extensive nevus comedonicus involving the palm: questionable role of the pilosebaceous unit in pathogenesis. Pediatr Dermatol. 2014;31(4):e96-e99.
5. Torchia D, Schachner LA, Izakovic J. Segmental acne versus mosaic conditions with acne lesions. Dermatology. 2012;224(1):10-14.
6. Ferrari B, Taliercio V, Restrepo P, et al. Nevus comedonicus: a case series. Pediatr Dermatol. 2015;32(2):216-219.
7. Tchernev G, Ananiev J, Semkova K, et al. Nevus comedonicus: an updated review. Dermatol Ther (Heidelb). 2013;3(1):33-40.