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An unexpected coexistence of two epidermal naevi on the scalp: Naevus comedonicus and naevus sebaceous

Epidermal naevi are cutaneous hamartomas originating from epidermis and adnexal structures. Classification of these hamartomas depends on the predominant cell type and the degree of cellular differentiation. Keratinocytic epidermal naevi have more epidermal differentiation, naevus sebaceus has more sebaceous differentiation, and naevus comedonicus involves hamartomatous follicular units. Although epidermal naevi are common, simultaneous presence of two at the same anatomic site is rare. Our patient presented with a striking lesion on the scalp exhibiting features of naevus sebaceus and naevus comedonicus both clinically and histopathologically. A 16-year-old boy presented with an asymptomatic, alopecic plaque on his scalp. He reported that he had noticed the lesion in early childhood. The lesion had started to enlarge at 10 years of age and gradually increased to the present size. No family members were known to have similar lesions. His routine laboratory findings were within normal limits. There was no neurological, skeletal, ophthalmological involvement or any other disorder. Physical examination revealed an alopecic plaque measuring 6 9 9 cm on the left temporoparietal region. The plaque had different components: irregularly shaped, salmon-coloured, waxy, rough areas and irregular papules which contain comedo-like openings filled with keratinous material and scar formation (Fig. 1). He had no specific subjective symptoms. Two 4-mm punch biopsies were obtained from the lesion. On histopathological examination, the salmoncoloured papules showed epidermal hyperplasia, presence of enlarged sebaceous glands located at an unexpected high level and associated directly with the surface of epidermis. These findings were consistent with naevus sebaceous (Fig. 2a,b). The comedo-like papules showed dilated follicles containing keratin material consistent with naevus comedonicus (Fig. 3a,b). We recommended excision of the lesion, but the patient declined treatment. Epidermal naevi are most commonly seen as isolated birthmarks. When extracutaneous abnormalities accompany epidermal naevi, it is referred as epidermal naevus syndrome. Naevus sebaceus is a relatively common type of epidermal naevi, accounting for approximately half. It is often present at birth and seen as a well-circumscribed, slightly raised, round or oval plaque. It has a salmon to yellow colour. In adolescence, under hormonal influences, the naevus widens and thickens, and its surface becomes waxy or verrucous. The predilection areas for NS are scalp and face. Naevus comedonicus is a rare hamartoma which may present at birth or develop later in life, mostly around the age of 10. It is characterised by numerous follicular openings filled with keratinous plugs. The distribution is usually unilateral and follows the Blaschko lines. Face, trunk and upper arms are the predilection areas. Scalp localisation is very rare. In the present case, naevus comedonicus and naevus sebaceus were localised on the scalp following the lines of Blaschko. We have been able to retrieve only two other reports of coexistence of the two different epidermal naevi. Kose and colleagues reported a young man with naevus sebaceus on his neck, naevus comedonicus on his lumbar area and a Becker’s naevus on his shoulder. Jung and colleagues described a 15-year-old girl who had naevus sebaceus on her left medial canthus and naevus