Morphogenesis of the cornoid lamella: histochemical, immunohistochemical, and ultrastructural study of porokeratosis.

To elucidate the morphogenesis of cornoid lamellae (CL) in porokeratosis, skin lesions of three cases of disseminated superficial actinic porokeratosis and a case of linear porokeratosis were examined. By N-(7-dimethylamino-4-methyl-3-coumarinyl)maleimide staining, SH groups were present in the living layer of the epidermis beneath CL and irregularly disappeared at the bottom of CL, whereas SS linkages appeared in dyskeratotic cells in the living layer and in the irregularly shaped cell membranes of the horny cells. Epidermis beneath CL showed an increased and irregular involucrin expression. Ultrastructurally, the living keratinocytes contained many cytoplasmic vacuoles and had a smaller number of lamellar bodies than normal. Intercellular lamellar sheets were incompletely formed. The dyskeratotic cells and the lower horny cells contained many small vacuoles but formed a marginal band. The horny cells of CL also formed a marginal band and, further, a keratin pattern. CL may be formed by hyperproliferative atypical kertatinocytes which keratinize rapidly and irregularly and show defective desquamation due to the paucity of intercellular lamellar sheets.