Intense eosinophilia with abnormal ultrastructure as presenting manifestation of acute lymphoblastic leukemia

A patient with acute lymphoblastife leukemia presented with intense eosinop hilia. Under the light microscope these eosinophils showed smaller eosinoph ilic granules and were detected as neutrophils by Coulter Gen-S cell counte r. This counter identifies cell morphology by size and forward and right an gle light scatter of cells. Under electron microscopy these eosinophils had smaller and fewer granules and very few crystalloid structures, thereby ex plaining the inability of the cell counter to identify them as eosinophils. Eosinophilia subsided at 6 months of treatment, i.e. 5 months after the pa tient went into morphological remission; cytogenetic and bone marrow analys es revealed no abnormality.