Two types of acquired idiopathic sideroblastic anaemia (AISA): a time-tested distinction

In 1982, acquired idiopathic sideroblastic anaemia (AISA) was included by the French-American-British (FAB) Co-operative Group in their classification of myelodysplastic syndromes (MDS). However, the malignant potentiality of AISA has always been a matter of debate. In different series, median survival and rates of transformation into acute myeloid leukaemia (AML) varied extensively. On cytomorphological grounds, AISA can be divided into pure (dyserythropoietic) sideroblastic anaemia (PSA), in which dysplasia is confined to erythropoietic cells, and a true myelodysplastic form (RARS), which is characterized by additional dysplastic features of granulopoiesis and/or megakaryopoiesis. In a previous study, based on retrospective analysis of 94 patients with AISA, we found that both types of sideroblastic anaemia differed considerably in terms of survival and risk of AML transformation. Almost identical results have now been obtained through a prospective study of 232 new patients with AISA. The difference in survival between PSA and RARS remained significant over the whole period of follow-up (survival after 3 years being 77% vs. 56%; P = 0.003), and the incidence of AML did not increase with time in the PSA group, even in the long term. This prospective study strongly supported our conclusion that cytomorphological distinction between PSA and RARS provides valuable prognostic information.