ULTRASTRUCTURAL OBSERVATIONS ON A VARIANT OF ACUTE PROMYELOCYTIC LEUKEMIA

A patient with acute leukemia is presented in whom the leukemic cells, as seen by light microscopy were typical promyelocytes. The cells had normal or slightly invaginated nuclei with typical cytoplasmic granul es and the diagnosis was confirmed by cytochemistry. The clinical cour se was rapid and the patient died of disseminated intravascular coagul ation and urosepsis within a few days of diagnosis. However, electron microscopic examination showed cells with extremely convoluted and lob ulated nuclei with nuclear pockets and cytoplasmic bridges as well as the complete absence of cytoplasmic granules in the majority of the ce lls. Furthermore, the urine lysozyme (muramidase) was elevated. These findings suggest that the leukemia in this patient may be classified a s a hypogranular variant of acute promyelocytic leukemia (APL), with m onocytoid ultrastructural appearances.