Ultrastructural examination of skin lesions from a typical case of Hand-Schüller-Christian disease showed evidence of a close resemblance to Letterer-Siwe disease. The cellular infiltrate was composed chiefly of abnormal histiocytes and Langerhans' cells. Most of the latter had a normal ultrastructural but abnormal histiocytes containing Langerhans' granules (that is, abnormal Langerhans' cells) were found in the cytoplasm. In a few nuclei of Langerhans' cells there were Langerhans' granules and other organelles, freely scattered or enclosed in vacuoles. Langerhans' cells were found crossing the basement membrane and others were undergoing mitosis within the epidermis.
Gianotti F, Caputo R. Skin Ultrastructure in Hand-Schüller-Christian DiseaseReport on Abnormal Langerhans' Cells. Arch Dermatol. 1969;100(3):342-349. doi:10.1001/archderm.1969.01610270084019