A case of histiocytosis X-central type. Histological, immunohistochemical and electronmicroscopical analysis

We report a case of Histiocytosis X (HX) associated with a high bone marrow and peripheral blood monocytosis in a 70 yr-old man. The histiocytic clusters in the skin showed the characteristics of epidermal Langerhans cells (LC): positivity for OKT6, OKIa1, ATP-ase and presence of Birbeck granules. Histiocytes in all other locations showed positivity for OKM1, OKIa1, acid P-ase and absence of Birbeck granules. The circulating monocytes were also negative for OKT6 and ATP-ase and lacked Birbeck granules. From these data we assume that the proliferation of monocytes in the bone marrow was the primary event, resulting in the release of large numbers of circulating monocytes and histiocytic proliferation in various tissues. These histiocytes acquired differing characteristics according to the microenvironment in which they underwent their final maturation. In the skin they differentiated into cells presenting the morphological, enzyme-and immunohistochemical characteristics of LC.