Leukaemoid reactions in myeloproliferative diseases. Report of two patients

The occurrence of transient extreme neutrophilic leucocytosis, with white blood cell counts exceeding 100,000/mu-l in two adult patients with myeloproliferative diseases, polycythaemia vera and acute myelocytic leukaemia in remission, is reported. The reaction was transient, and the subsequent course of the patient's disease did not differ from that prior to the episode. Such extreme leucocytosis is rare in adults, despite the frequency of provoking conditions, and factors which predispose an individual to develop a leukaemoid reaction remain unknown. An increase in the size of the pool of proliferating granulocyte precursors accompanied by a loss of the restraining function of the marrow sinusoidal walls in myeloproliferative diseases may explain the augmented release of myeloid cells in our patients.