The initial classification of the myelodisplastic syndromes (MDS) was compiled in 1976 by the FAB group and was based on morphological parameters observed in the peripheral blood and in the bone marrow. The FAB classification was revised in 1982 and has been used in the last 25 years as a guide for a better understanding of this heterogeneous group of diseases. In 2001, the WHO published a new classification with significant modifications in the diverse subgroups of FAB with the intention of obtaining a better grouping of the subtypes with similar clinical behaviors. The most important modification was the decrease in the minimum number of blasts for the AML diagnosis from 30% to 20%, resulting in the disappearance of the subtype RAEB-T. This is also the most polemic alteration, as there are innumerable publications discussing the evident clinical and biological differences between the MDS and AML, with the opinion that the number of blasts alone is insufficient for the choice of therapy being unanimous. Another important point was the differentiation of the groups with dysplasia in single and multiple strains, which has been demonstrated as having great importance in the prognosis. Several studies have been published comparing the FAB and WHO classifications, recognizing the great contribution of the FAB classification for the better understanding of the MDS, as well as its shortcomings, and attempting to validate the modifications proposed by the WHO classification and identify the points liable to modification.
Myelodisplastic syndrome; morphological classification; dysplasia; prognostic factors
