The pathology of adult type Letterer-Siwe disease.

Large globular histiocytes infiltrated the papillary region of the dermis with little tendency to extend deeper than the subpapillary vascular plexus. Histiocytes penetrated the basement membrane and colonized the epidermis causing disruption with formation of haemorrhagic crusts. Groups of histiocytes within the epidermis give an appearance similar to that of Paget's disease. The histiocytes were large and rounded with "shaggy" margins and fairly distinct copius cytoplasm. Both Langerhans' cells and histiocytosis X cells fail to become strongly phagocytic under ordinary conditions in lymph nodes and in the skin. None the less, these cells show some of the characteristics of phagocytes with migratory ability, adhesion to glass, apposition to Lymphocytes and a variable hydrolytic enzyme content.