Sir,

Sebaceous nevus (SN) is a benign congenital hamartoma due to abnormalities of the epidermis, sebaceous glands, apocrine glands, and hair follicles.

Clinically, it presents as a sharply circumscribed yellow-orange hairless plaque that is usually located solitarily linear in configuration and mainly situated on the face and scalp. It is often sporadic cases but familial ones have been reported [1].

The natural history of sebaceous nevus is traditionally divided into 3 evolutionary stages.

The childhood stage is characterized by a quiescent waxy yellow plaque and underdevelopment of the hairs and sebaceous glands.

During the puberty stage, lesions become gradually elevated, verrucous, or nodular. Histologically, masses of hypertrophic sebaceous glands with papillomatosis and hyperkeratosis of the overlying epidermis occur.

The neoplastic phase, complicating the development of benign or malignant tumors can be seen arising from the NS usually in late adult life [1].

The secondary neoplasms include syringocystadenoma papilliferum (SCAP), trichoblastoma, trichilemmoma, apocrine cystadenoma, trichilemmal cysts, basal cell carcinoma, sebaceous carcinoma, squamous cell carcinoma. The most common ones are trichoblastoma and SCAP. However, malignant neoplasms are uncommon, and BCC is the most frequent one [2].

A study concluded that trichoblastomas and trichilemmomas were the two most frequent secondary neoplasms [3]. However, pilomatrixoma was not reported. Even in other large series of sebaceous nevus, there were no records of it associated with sebaceous nevus [4]. We describe a unique case of a pilomatrixoma arising from sebaceous nevus.

A 15-year-old child who presented since birth with a yellowish lesion surmounted by a nodule progressively increasing in size which motivated her consultation.

Clinical examination found a yellowish filiform verrucous plaque roughly oval measuring 3 cm in long axis surmounted by a well-limited round erythematous nodule of firm consistency measuring 3 cm in diameter (Fig. 1a). Dermoscopy showed irregular linear vascularization with an erythematous background (Fig. 1b). Chirurgical excision confirmed a sebaceous nevus complicated with pilomatrixoma.

Figure 1: (a) Clinical image showing a yellowish filiform verrucous plaque roughly oval measuring 3 cm in long axis surmounted by a well-limited round erythematous nodule of firm consistency measuring 3 cm in diameter. (b) Dermoscopy showed irregular linear vascularization with an erythematous background.

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