Use of Transmission Electron Microscopy in Diagnosis of Acute Leukemias: A Prospective Study of Fifty Cases.

Ultrastructural studies have contributed substantially to the understanding of the cellular morphology of the acute leukemias. We present here 50 cases (aged 3-55 years, M: F-32: 18) of acute leukemias, which were studied for morphology, conventional cyto chemistry, immunophenotyping, and transmission electron microscopy (TEM) including ultrastructural cytochemistry using myeloperoxidase (MPO) and platelet peroxidase activity. TEM morphology using ultrastructural cytochemistry of MPO helped diagnose three cases of acute myeloid leukemia with minimal myeloid differentiation (AML M0). The blasts showed large round nuclei, 1–2 nucleoli, chromatin with peripheral condensation and abundant mitochondria. Of total of 5 cases of acute promyelocytic leukemias (APML), all had strong Sudan Black, MPO, dual esterase positivity; one case was non-specific esterase positive and sensitive to fluoride. On TEM, this unusual case was identified to be microgranular variant of APML. TEM morphology and ultrastructural cytochemistry using platelet peroxidase helped diagnose 3 cases of AML M7 (acute megakaryocytic leukemia), 2 cases of acute biphenotypic leukemias and also in differentiating one case of acute proerythroblastic leukemia (AML M6b) from 3 cases of AML M6a or acute erythroleukemia. Thus, TEM is helpful in differentiating further the subgroups of AML-M5 and AML-M6, in identifying the microgranular variant of APML, and in confirming the diagnosis of AML-M0 and biphenotypic leukemia. Also, in cases with very hypercellular marrow and with associated myelofibrosis, where the bone marrow aspiration gives low cell count, TEM and ultrastructural cytochemistry are a valuable aid to arriving at a accurate diagnosis.