A unique cytoplasmic structure in papular histiocytoma

In benign and malignant histiocytic proliferations of the skin, electron microscopy has revealed various cytoplasmic structures including Langerhans granules, worm like bodies, dense bodies, and myelinated bodies whose nosologic role has been given different interpretations. In 1974 Rodriguez et al. described a case of nodular cutaneous reactive histiocytosis 'exhibiting' pleomorphic cytoplasmic inclusions never observed before. In 1975 Touraine et al. (unpublished data) found the same cytoplasmic structures in a case of unclassified histiocytosis and Degos et al. made similar observations in a case of multicentric reticulohistiocytoma. In 2 cases of papular histiocytosis light and electron microscopic analysis of biopsy specimens of the lesions revealed a large number of cells containing granules identical to those reported by others. The intracytoplasmic granules with a unique and highly complex ultrastructure, were found in the cellular infiltrate of the 2 patients with papular histiocytosis. Examination of serial sections enabled the construction of a three dimensional model of these granules, which appear to be composed of an elaborate arrangement of membranes and vesicles. Two hypotheses (endocytosis and exocytosis) are proposed for the mode of formation of these unique cytoplasmic structures.