Verrucous pilar cysts infected with beta human papillomavirus.

Epidermoid cysts with histopathologic features of human papillomavirus (HPV) infection have been previously reported and are commonly termed verrucous cysts. We report a series of eight histopathologically distinct verrucous pilar cysts, distinguished from traditional verrucous epidermoid cysts by trichilemmal keratinization, as well as two verrucous hybrid pilar-epidermoid cysts. These lesions contain characteristic stratified epithelial linings with abrupt transitions to compact eosinophilic keratin, as well as areas of papillomatosis, coarse intracytoplasmic keratohyalin granules, and vacuolar structures suggestive of HPV-induced cytopathic change. HPV-24, a β genus HPV species, was identified by degenerate polymerase chain reaction in DNA extracted from two of the lesions, and the presence of β-HPV E4 protein was confirmed by immunohistochemistry. HPV-60, the HPV species most commonly reported in verrucous epidermoid cysts, was not detected. Verrucous pilar cysts represent histopathologically and potentially etiologically distinct lesions which may be underrecognized.