Myelodysplastic syndrome (MDS) is frequently associated with monocytosis in the blood and myelomonocytic dysplasia in the bone marrow. In two groups of patients with MDS, all subtypes excluding CMML, the authors demonstrated that monocytosis was present in 15% of the patients in group I according to the haemogram at the time when the diagnosis was established and in 19% in group II where it was required that at least in half the haemograms throughout the course of the disease there were more than 10% monocytes. No difference was found in the prognosis of patients with monocytosis, as compared with patients with monocytopenia as regards the life span and frequency of transformation into AL. The cytogenetic and cultivation findings did not differ either. In some instances, in particular in patients with RA and RAS significant monocytosis was not associated with the expected proliferation of monocytoid cells in bone marrow. The authors assume that proliferation and differentiation of germ cells in the monocytic series is easier than in the granulocytic series and that monocytosis can be considered a manifestation of substituted neutropenia. The work indicates the difficulties associated with the differential diagnosis of RA, RAS and RAEB with monocytosis, MDS with a dominating change of the type of myelomonocytic dysplasia and CMML proper.

Keywords: Anemia, Refractory /blood/; Anemia, Sideroblastic /blood/; Bone Marrow /pathology/; Humans; Leukocyte Count; Monocytes /pathology/; Myelodysplastic Syndromes /blood/