Haematological Aspects of Drug‐Induced Agranulocytosis

Haematological disorders were studied in 26 patients who survived 30 attaks of acute agranulocytosis (24 due to pyrazolone derivatives and 6 to antithyroid drugs). Sixty-three samples of the bone marrow were analysed, retrogradely, from the day when the number of blood granulocytes reached its normal level (the ‘day of recovery’). In early phasis of agranulocytosis, an aplasia of granulocytic and erythroid series was noted, the megakaryocytopoiesis remaining unaffected. The promyelocytic-myelocytic marrow, a cytological phenomenon to which the term ‘maturation arrest’ has been applied, was found to precede the reappearance of granulocytes in peripheral blood. It is confirmed that acute agranulocytosis is the result of bone marrow damage which leads to a stop in the production of granulocytes. It is shown also that red cell production is stopped but the long survival of erythrocytes accounts for the absence of anaemia. The promyelocytic-myelocytic marrow, erroneously termed ‘maturation arrest’, represents a step in regeneration of granulocytopoiesis and reflects an intensive proliferative activity of granulocytic series.