Acute leukemia with unusual cytoplasmic inclusions: a cytochemical and ultrastructural study.

A 76-year-old woman with acute leukemia responded incompletely to prednisone and vincristine. Cytochemistry of the blast cells demonstrated only focal alpha-naphthyl acetate and alpha-naphthyl butyrate esterase activity and focal coarse granular beta-glucuronidase activity, a pattern usually associated with acute lymphocytic leukemia. Electron microscopy demonstrated primitive cells with features usually associated with promonocyte differentiation including prominent parallel arrays of microfilaments and nucleoli of the nucleolonema type. In Wright-stained films, blasts contained oval, pale-blue, yellow tinged cytoplasmic inclusions about 2 to 4 micrometers in diameter which did not stain with any of the cytochemical methods employed. With electron microscopy, these inclusions were nonmembrane bound structures, varying from amorphous electron dense stippling to irregularly arranged short segments of filaments to prominent parallel arrays of filaments. We propose that the inclusions may have arisen from the parallel arrays of microfilaments and are nonspecific.