Acute leukemia of adults. Ultrastructural, cytochemical and histologic observations in 100 cases.

In order to establish guidelines for categorization of acute leukemia, marrow histology, special stains, and electron microscopy were performed in 100 adult leukemia cases. Differential counts for each stain were performed, and the results were combined with those obtained by electron microscopy for final classification. Myeloid (non-lymphoid) leukemia was most common (83 cases), and there were 13 lymphoid cases, two cases of erythroleukemia, and two undifferentiated leukemias. Histologic studies of marrow particles revealed significant admixtures of lymphocytes, plasma cells, and abnormal erythroid elements, particularly in acute myelomonocytic leukemia. Interpretations of cytochemical results were confirmed by ultrastructural studies in 90% of the cases. Clinically significant discrepancies between cytochemical and ultrastructural interpretations were rarely found. Only two myeloid and five lymphoid cases did not mark typically with any cytochemical stain. The single most reliable special stain was the periodic acid-Schiff stain, whereas the stain most difficult to interpret was the alpha-naphthyl acetate esterase stain. Sudan black stain was particularly helpful in demonstrating Auer rods. Five of six cases unclassified by cytochemistry were categorized by electron microscopy. Although patterns of cytochemical staining were delineated for each type of leukemia, significant intragroup variation in cytochemical reactions was recognized. This study indicates that ultrastructural examination should be routinely used for categorization of cases with equivocal cytochemical findings and for analysis of unclassified cases.