Quiz

Acta Derm Venereol 2019; XX: XX–XX.

Diagnosis: Naevus comedonicus of the scalp

Skin biopsy revealed a hyperkeratotic epidermis with cup-shaped follicular plugging (Fig. 2). Arrector pili muscles and sebaceous glands were absent. A diagnosis of naevus comedonicus (NC) was made based on the clinical and histological findings. The patient was referred to plastic surgery for treatment. The lesion was excised successfully with no complications.

NC is a rare subtype of epidermal naevus first described by Kofmann in 1895 (1). It has been considered a hamartoma of the pilosebaceous unit, resulting in developmental defect in production of mature hairs, matrix cells, or sebaceous glands. Only soft keratin can be formed, which results in dilated follicular orifices (2). Somatic mutation of the fibroblast growth factor receptor 2 gene (FGFR-2) is thought to be an important factor in the pathogenesis of NC (3). NC can be associated with central nervous system, ocular and skeletal abnormalities in the context of naevus comedonicus syndrome (4).

Clinically, the lesions of NC may present shortly after birth or may develop during early childhood (most commonly before the age of 10 years) (5). Growth of the lesions appears to be proportional to age, but may be accelerated during puberty due to the increase in eccrine and sebaceous secretions (4). NC is characterized by multiple asymptomatic dilated follicular openings with dark keratinous plugs resembling comedo-like lesions in a linear, unilateral distribution along Blaschko’s lines or presenting as a circumscribed plaque. Occasionally, it may associate with bacterial infections, drainage, cyst formation, and scarring, which is an inflammatory subtype of NC (6). The lesions are most commonly located on the face, neck, trunk and upper extremities. Involvement of the palms, soles and genitals has also been reported. However, involvement of the scalp is extremely rare (2, 6–8). Histology typically reveals grouped immature follicles with dilated keratin-filled invagination of the epidermis, devoid of hair shafts or well-formed sebaceous glands (7). Immunohistochemical findings showed an increased expression of proliferating cell nuclear antigen (PCNA), intercellular adhesion molecule-1(ICAM-1), HLA-DR and CD68 (9). Clinical differential diagnosis includes acne conglobata, naevus sebaceous, epidermal naevi, Favre-Racouchot syndrome and familial dyskeratotic comedones.

NC are thought to be have a benign course, but association with squamous cell carcinoma has been reported recently; thus surgical treatment or close monitoring of these patients is recommended (10). Other treatment options include systemic retinoids, topical therapy (retinoic acid, salicylic acid, 12% ammonium lactate) and ablative laser treatment (ultrapulse carbon-dioxide lasers, erbium-YAG lasers, 1450-nm diode laser), which have been used with various success (5, 8).