Papillomavirus-infected keratinous cyst on the sole. A histologic, immunohistochemical, and electron microscopic...

A 17-year-old boy had a keratinous cyst on the sole. The keratinous cyst and its overlying epidermis had solitarily scattered keratinocytes, which contained a peculiar intracytoplasmic inclusion body above the lower spinous layer. Immunohistochemistry and electron microscopy revealed that the nuclei of these cells had virions of papillomavirus. These virions appeared above the spinous layer. The inclusion bodies were highly eosinophilic masses in the viable layer, and slightly basophilic, fine granules in the cornified layer. Their number at any time was usually one. Their histologic and ultrastructural features and their N-(7-dimethylamino-4-methylcoumarinyl)-maleimide staining property were different from those of keratohyalin and from those of amyloid or hyaline body. Also the keratinous cyst was associated with colloid bodies, showing the lamellated figure in the subepithelial area.