Pagetoid reticulosis: a disease of histiocytic origin.

A patient with Pagetoid reticulosis has been investigated using standard transmission electron microscopy and an immunohistochemical technique for identifying T lymphocytes in situ in light and electron microscopy. Our results indicate that the majority of the cells in the underlying dermal infiltrate are T lymphocytes but that only very few T lymphocytes are found in the extensive epidermal infiltrate. Ultrastructurally the majority of the abnormal cells in the epidermis are of histiocytic origin.