A cytochemical and ultrastructural study of acute myelomonocytic leukemia exhibiting the pseudo-Chediak-Higashi anomaly of leukemia and "splinter-type" Auer rods.

An unusual case of acute myelomonocytic leukemia (AMML) in an 81-year-old man is described. Ultrastructural examination revealed the presence of distinct Auer bodies, which commonly are found in acute promyelocytic leukemia (APL). The Auer bodies had a splinterlike appearance with a distinct tubular substructure. The morphologic appearance of the leukemic cells coupled with the results of cytochemical staining reactions (alpha-naphthyl AS-D chloroacetate esterase, alpha-naphthyl butyrate esterase, Sudan black B, and periodic acid-Schiff reaction) identified this leukemia as myelomonocytic in origin. APL-like Auer rods in AMML now can be included in the spectrum of morphologic forms commonly seen in myelogenous leukemia and lends support to the hypothesis of an aberrant stem cell. In addition to the APL-like Auer rods, the leukemic blasts contained giant pink-staining granules on Wright's stain, some of which had a tubular substructure similar to the Auer rods under the electron microscope. The presence of these megagranules is a morphologic aberration termed "the pseudo-Chediak-Higashi anomaly of acute leukemia," and now has been described for the first time in AMML at the ultrastructural level.