Pigmented viral warts: a clinical and histopathological study including human papillomavirus typing

Although clinical, histological and viral correlations have recently been established among pigmented warts, homogeneous intracytoplasmic inclusion bodies and related types of human papillomavirus (HPV) (HPV 65, 4 and 60), the causes of the pigmentation remain unknown. In this study, comparative histological and histochemical analyses were performed with 53 pigmented (34 HPV 65-induced, 12 HPV 4-induced and seven HPV 60-induced) and 73 non-pigmented warts (27 HPV 2-induced, 23 HPV 1-induced, 12 HPV 63-induced, six unknown HPV-type induced and five HPV 60 induced) to clarify the causes of the pigmentation. Electron microscopy was also used to examine the pigmented warts. Many melanin blockade melanocytes were identified in all of the pigmented warts with Masson-Fontana staining and electron microscopy, and increased melanin in keratinocytes was also noted in 22 pigmented warts, suggesting that the dispersion of melanin granules in the dendrites of the melanin blockade melanocytes and the increased melanin granules in keratinocytes are the primary contributors to the pigmentation of the warts. The homogeneous intracytoplasmic inclusion bodies might also play a part in the darkening of the warts, as only the cases which had the inclusion bodies as well as the melanin blockade melanocytes were clinically pigmented. Although melanin blockade melanocytes were seen in a few cases of HPV 1- and HPV 2-induced warts in which the homogeneous inclusion bodies were not observed, the warts were not clinically pigmented. Melanin blockade melanocytes were not seen in any of the HPV 63-induced non-pigmented warts. In conclusion, the pigmented warts were associated with one of the related types of HPV (HPV 65, 4 and 60), and the pigmentation of the lesions is thus thought to be caused primarily by melanin blockade melanocytes. The homogeneous intracytoplasmic inclusion bodies might also play a part in the darkening of the lesions. This is the first report dealing with the pigmentary disorder associated with specific types of HPV.