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Keratoacanthoma arising in nevus comedonicus

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Keratoacanthoma arising in nevus comedonicus
Sara Zarkik MD, Jamila Bouhllab MD, Aicha Methqal MD, Yassir Afifi PhD, Karima Senouci PhD, Badreddine Hassam PhD
Dermatology Online Journal 18 (7): 4

Department of Dermatology, Avicenne University Hospital, Rabat, Morrocco


Nevus comedonicus is a benign hamartoma of the pilosebaceous unit and is considered as a rare subtype of epidermal nevus. It was first described in 1895. It manifests as a group of closely dilated follicular openings with dark keratin plugs resembling comedones. Malignant degeneration of a nevus comedonicus is exceptional; we report a case of keratoacanthoma arising in extensive nevus comedonicus.


Nevus comedonicus is a benign hamartoma of the pilosebaceous unit and is considered a rare subtype of epidermal nevus. It was first described in 1895 by Kofmann [1]. It manifests as a group of closely dilated follicular openings with dark keratin plugs resembling comedones. We report the first case of keratoacanthoma arising in extensive nevus comedonicus.

Case report

A 20-year-old man presented with asymptomatic grouped comedo-like keratin filled pits on the right lower limb since his birth. The lesions grew with the patient's growth, but faster during puberty. There was no history of a similar case in the family.

Figure 1Figure 2
Figure 1. Linear disposition of nevus comedonicus

Figure 2. Keratoacanthoma arising in nevus comedonicus

Figure 3
Figure 3. Groups of comedo-like keratin filled pits

Examination revealed multiple groups of dilated pilosebaceous orifices filled with black keratin plugs arranged linearly along the posterior side of the right lower leg. Some cutaneous lesions in the middle of the hamartoma began burgeoning when he was 18 years old. Lesions were asymptomatic, unilateral, and irregularly scattered throughout the skin. The soles, palms, and mucosa were spared and regional lymph nodes were not palpable. The skin biopsy of the budding area revealed a keratoacanthoma.

Figure 4Figure 5
Figures 4 and 5. H&E-stained sections, magnification shows a crater lesion with lateral spur and depression filled with keratin. Pseudoepitheliomatous hyperplasia is seen and in the surrounding dermis a moderate mononuclear cell infiltrate is present.

Because of the size and location of the lesion surgery was not advised for this patient. Therefore, we opted for methotrexate (25 mg intramuscular weekly). Regression of the lesion was observed over two months of treatment.


Nevus comedonicus usually arises before the age of 10; it is present at birth in almost half of the cases. The majority of cases are solitary. However, this hamartoma may be part of nevus comedonicus syndrome in association with skeletal anomalies (scoliosis, fused vertebrae, spinabifida occulta, absent fifth finger) or central nervous pathologies (seizures, changes noted on EEG, transverse myelitis), ocular alterations (cataracts) [2], and cutaneous defects (multiple basal cell carcinoma) [3]. Our patient did not have any systemic findings.

Nevus comedonicus is evident clinically as confluent clusters of dilated follicular orifices plugged with keratin, giving the appearance of aggregated open comedones. These clusters are often arranged in a linear or zosteriform pattern, occasionally in parallel with the lines of Blaschko. Although usually unilateral, bilateral occurrences have been noted. As with other epidermal nevi, the most common sites are the face, trunk, and proximal extremities.

The pathogenesis of NC remains obscure. Immunohistochemical studies show that filaggrin is involved in the formation of closed comedones and may be involved in the pathogenesis of abnormal keratinization in nevus comedonicus [4].

Comedo nevus is a benign lesion and does not need treatment unless the patient requires it for aesthetic reasons or has a complication. Treatment options for nevus comedonicus include antibiotics for inflamed or infected lesions, topical keratolytics, topical retinoic acid (0.025% - 0.1%), 12 percent ammonium lactate lotion, calcipotriene, oral retinoids, dermabrasion, superficial shaving, or surgical excision [5, 6]. Also, the use of erbium: YAG [7] and CO2 laser has been reported [8]. Our patient was treated in his childhood by topical retinoids, but without any remarkable improvement.

Epidermal nevus has been associated with benign and malignant neoplasms [9, 10], but malignant degeneration of nevus comedonicus is exceptional. Literature reports only one case of squamous cell carcinoma on a facial nevus comedonicus [11]. The present case is characterized by the appearance of keratoacanthoma in a very extensive nevus comedonicus. Keratoacanthoma is a fairly common neoplasm among light-skinned people. It was once considered a pseudomalignancy that resembled squamous cell carcinoma. It is now considered to be a squamous cell carcinoma that resembles a pseudo-benign tumor [12]. Our patient responded well to methotrexate.


From this paper and based on this case we recommend a close surveillance of this kind of hamartoma in order to detect malignant degeneration.


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