[Myelodysplastic syndromes: unusual and mild forms]

Although the FAB classification of the myelodysplastic syndromes (MDS) allows to classify most patients, a few clinical patterns do not fit the FAB categories, including borderline forms with manifestations usually seen in other diseases and forms with atypical or unusual clinical or laboratory features that do not immediately suggest a MDS. Borderline forms are characterized by the presence of any of the following: high or very high platelet counts, myelofibrosis, bone marrow hypoplasia, eosinophilia, or systemic diseases such as relapsing polychondritis. Unusual or atypical forms include manifestations such as hemolysis, high reticulocyte counts, erythroblastopenia, or an abnormality of a single cell line such as isolated thrombocytopenia, isolated neutropenia, or isolated macrocytosis. The definitive diagnosis of these forms of MDS can require a number of investigations such as cytogenetic studies, bone marrow biopsy, and/or radionuclide evaluation, and may not be possible until the patient has been followed for some time.