Histiocytosis and a leukaemoid response. A case report.

A patient with all the clinical signs of Letterer-Siwe disease is reported. The patient was unusual in that he had a severe leukaemoid reaction. To our knowledge, only 2 similar patients with reticulo-endotheliosis, histiocytic skin infiltration and leukaemoid reaction have been reported. It is possible that the disorder may represent a variant of the histiocytic proliferative disorders, characterized by both histiocytic and myeloid hyperplasia, and is thus similar to myelomonocytic leukaemia. However, it differs from the latter condition in that there is proliferation of monocytes and granulocytes in soft tissues rather than in the blood.