Verrucas or condyloma are common, benign, contagious epithelial tumours caused by infection with human papillomaviruses (HPV).
Verruca plana are benign, slightly elevated, flat-topped, smooth papules and relatively common in children, adolescents and young adults. Etiological association is mainly with HPV-3 and HPV-10. Flat warts are preferentially located on the back of the hands and fingers, distal forearm, lower leg and face. They are usually smaller than common warts and typically manifest as small round to oval epidermal papules measuring 1-4 mm in diameter. The number ranges from one to several hundred and the distribution is sometimes linear (Koebner phenomenon).
Histology reveals a loose hyperkeratosis with basket-weave-pattern but little or no papillomatosis as in verruca vulgaris. Superficial epidermal layers show koilocytosis, vacuolated keratinocytes with perinuclear clearing around centrally located nuclei (so-called “birds-eye cells”) and hypergranulosis. Regression of plane warts may occur after years and is accompanied by a superficial lymphocytic infiltrate
LeBoit PE, Burg G, Weedon D, Sarasin A (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Skin Tumours
IARC Press: Lyon 2005
Flat wart-like lesions can be encountered in patients with epidermodysplasia verruciformis. These lesions may show a typical blue-grey cytoplasm.