Eosinophilia in systemic mastocytosis.

The diagnosis of systemic mastocytosis depends on the proper recognition of extensive mast cells infiltration in tissues. Accurate identification of the mast cells in tissues may be difficult when there is no clinical suspicion to initiate a special search for these cells. Four patients with atypical clinical features and eosinophilia in tissues and three with eosinophilia in blood had hematologic or histologic findings suggestive of myelofibrosis with myeloid metaplasia, and malignant lymphoma. It was the presence of blood and tissue eosinophilia in these patients that led to further investigation and recognition of the diagnosis of systemic mastocytosis. Methods for identification of the mast cells are examined. The combined use of Wright-Giemsa stain, toluidine blue, and aminocaproate esterase is preferred. The eosinophils are intimately related to the mast cells. In cases of eosinophilia of unknown etiology, systemic mastocytosis should be considered one of the possible etiologic factors.