Extensive epidermal naevus in a foal

A 2-month-old Standardbred filly was presented for examination and treatment of extensive congenital skin lesions that had a linear distribution on the left front leg extending from the dorsal midline to the metacarpal region. The lesions were surgically excised under general anaesthesia. Surgical excision was curative and there were no signs of recurrence 6 weeks after surgery. The number and distribution of lesions were more extensive than in previously reported cases of congenital papillomas, which have also been described as epidermal growth abnormalities (naevi or hamartomas). Early reports of congenital papillomas suggest in-utero infection with papillomavirus may be responsible, despite a lack of histological features associated with papillomavirus infection. Papillomavirus immunohistochemistry has subsequently proven negative in tested cases.

The presence at birth, their appearance and the extensive distribution of lesions in this case is similar to verrucous epidermal naevus of humans. A name change from congenital papilloma to epidermal naevus is proposed for this condition in horses.