Seborrhoeic keratosis

Definition/diagnostic criteria Seborrhoeic keratosis (SK) is a benign overgrowth of epidermal keratinocytes. It is characterised by an irregular verrucous surface, a greasy appearance and a ‘stuck-on’ look, where the lesion seems to sit on top of normal skin. Lesions vary in colour from brown to black, with thinner lesions being paler, and traumatised lesions appearing inflamed. They usually measure 1-3 cm in diameter, although some can be larger​​.

Epidemiology SKs are very common in the UK, with more than half of men and more than a third of women having at least one. By the age of 40, about 30% of the population are affected, and this increases to 75% by the age of 70. The incidence of SKs varies from person to person​​.

Diagnosis SKs are typically diagnosed based on clinical features. They are commonly found on the trunk and face, but can arise on almost any body site.

• Symptoms are usually absent, but they may occasionally itch or come away with minimal trauma.
• Lesions can be flat, raised or pedunculated, and vary in color from yellow to dark brown.
• Dermoscopic features of SKs include acanthotic SK with thickened epidermis, multiple fissures and ridges, and grouped skin-coloured globules.
• Histological examination reveals a localised proliferation of the basal layer of the epidermis with hyperkeratosis in the surface crypts​​​​.

Treatment Most SKs do not require treatment. However, when necessary, the majority can be treated with liquid nitrogen (cryosurgery). Very thick lesions are best removed by curettage and cautery, with all samples sent for histology. Superficial cryotherapy is usually adequate if treatment is required.

In cases of diagnostic uncertainty, urgent referral to secondary care is advised​​​​.

Prognosis SK is a benign condition and does not typically necessitate intervention unless for cosmetic reasons or if there is diagnostic uncertainty. There is no evidence to suggest that SKs have a significant impact on long-term health outcomes.