What is nevus comedonicus?Nevus comedonicus (comedo nevus) is a rare hamartoma of the pilosebaceous unit. It is considered as an abnormal differentiation and development of follicular structures. The failure of the folliculosebaceous unit to develop properly, results in its inability to form hair or sebaceous glands. Only keratin is produced which accumulates in the dilated pores as comedo-like keratinous plugs.
Clinical CharacteristicsNevus comedonicus (NC) is a rare type of epidermal nevus, characterized by dilated follicular ostia (openings) with comedo-like keratinous plugs. The comedo-like lesions are closely arranged in a honeycomb pattern. Though these lesions are asymptomatic with acne-like characteristics, in some cases there may be inflammation and formation of suppurative cysts, papules, pustules and abscesses. The lesions tend to grow more quickly at puberty.
Nevus comedonicus lesions present, unilateral, bilateral, linear, plaque-like, interrupted, zosteriform, segmental or Blaschko linear pattern of distribution. The intervening skin may appear normal or show hypertrophy and hyperkeratosis. These comedo-like cysts have a predilection for the face and neck region. In rare cases they may affect other parts of the body, including scalp, genitalia, trunk, limbs, palms and soles.
Who can get nevus comedonicus?These comedo lesions develops shortly after birth and in most of the patients they tend to occur before the age of ten years. In rare cases adults may also develop these comedo-like lesions. There is no gender or racial predilection. The presence of NC in several families has been documented. The occurrence of nevus comedonicus in homozygous twins has been reported. The prevalence of this disorder has been estimated to be 1 in 45,000 to 100,000 individuals.
What causes nevus comedonicus?These lesions are considered as hamartoma caused by abnormal differentiation and development of follicular structures. The exact etiology of these comedo lesions is unclear. As nevus comedonicus can occur congenitally a genetic mosaicism has been proposed. However, the cause of its occurrence late in life is not known. Though generally considered as a failure of folliculosebaceous unit to develop properly, the presence of comedo nevus in a palm or sole indicates the sweat duct dilatation with keratin plugs in the opening.
Diagnosis of comedo nevusDiagnosis of nevus comedonicus may be made by physical examination and dermoscopy. A magnetic resonance imaging review may help in the diagnosis of nevus comedonicus. Skin biopsy may also help to confirm the diagnosis. Histologic studies of comedo cysts will reveal absence of sebaceous glands or their rudimentary presence. The hair follicles will appear underdeveloped and devoid of hair shafts. Nevus comedonicus has to be differentiated from similar-looking ailments like acne vulgaris, familial dyskeratotic comedones, lichen striatus and keratosis pilaris.
ComplicationsThese comedonicus lesions may develop into multiple masses with typical cysts containing keratinized tissue. Inflammatory form of comedo nevus may lead to formation of suppurative cysts, papules, pustules and abscesses with repeated bacterial infections and drainage. Such comedo lesions can cause formation of scar tissue.
Nevus comedonicus treatmentAsymptomatic benign comedo-like lesions does not require treatment, except for cosmetic and aesthetic reasons.
Conservative treatment options include application of emollients, moisturizers and keratolytics. Salicylic acid, or 12% ammonium lactate solution may be applied to dissolve the keratinous plugs and improve the cosmetic appearance. Superficial shaving, comedo extraction, or dermabrasion are some of the treatment methods giving mixed results and the recurrence of comedo-like lesion is very common.
Inflamed comedo nevus may require application of topical corticosteroids. Limited results were achieved with the topical application of anti-comedo retinoid agents like topical tretinoin and tazarotene. Oral retinoids like isotretinoin were found to be ineffective in most cases of comedo-like lesions. Complete resolution of NC can not be achieved by treatment with topical or oral retinoids and relapses are common.
Localized comedo-like lesions can be surgically removed with successful results. Radical resection may be necessary to remove large, multiple comedo cysts and prevent their further invagination. Long linear lesions, especially on limbs, removed by surgical excision require complex decongestive treatment to support and enhance healing process. Large and extensive comedo lesions will require skin transplants for defect closure.
Laser treatments with 2,940-nm erbium YAG, 10,600-nm ultra-pulsed CO2, or 1,450-nm diode lasers had shown promising results. However skin depressions occur. There may be delayed relapse of nevus comedonicus.
Nevus comedonicus syndrome (NCS)NCS is a neurocutaneous disorder manifesting with symptoms such as comedo-like lesions, leukoderma, lichen striatus, abnormalities of central nervous system, cataracts, scoliosis, fused vertebrae, limb deformities and spina bifida. Nevus comedonicus syndrome is also associated with benign epithelial tumors like trichoepithelioma (hair follicle tumors), keratoacanthoma (a low-grade skin tumors), syringocystadenoma papilliferum (an adnexal skin tumor) and hidradenoma papilliferum (a tumor occurring in the anogenital region of adult women). In very rare cases nevus comedonicus syndrome may be associated with basal-cell cancer (BCC) or squamous-cell cancer (SCC).
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