Transient granulocyte maturation arrest: discovery by flow cytometry of a variant form of agranulocytosis.

A 5-year-old child presented with pneumonia and agranulocytosis. A Wright-stained peripheral blood smear showed only cells which had the morphological appearance of lymphocytes, plus a few monocytes and eosinophils. A bone marrow aspirate smear showed a complete lack of recognizable granulocyte precursors. However, the admission CBC and differential performed by automated flow cytochemistry (Technicon Instruments Corporation H-6000) measured 32% granulocytes as determined by peroxidase activity. Cytochemical stains on the blood and marrow smears revealed that many of the cells that had the morphological appearance of lymphocytes were positive for myeloperoxidase activity. Special studies on these cells revealed them to be abnormal, intermediate granulocytes with azurophilic, peroxidase-containing primary granules, but with few secondary granules and limited lactoferrin activity. Over 28 days the child recovered, first with granulocytic hyperplasia in the marrow and then a return of the peripheral blood to normal. This is the first case report of an episode of transient "agranulocytosis" which in reality was a maturation arrest.