Introduction

The chronic myeloid disorders, which become more prevalent with age, can be categorized as either bcr/abl-positive (ie, positive for the Philadelphia chromosome, which is characteristic of chronic myelocytic leukemia) or bcr/abl-negative. The bcr/abl-negative chronic myeloid disorders can be subdivided into the chronic myeloproliferative disorders (see Table 71-1 and Figure 71-1) and the myelodysplastic syndromes. The classic myelodysplastic syndromes include refractory anemia and chronic myelomonocytic leukemia.

However, not all myeloid processes can be categorized as myelodysplastic syndromes or chronic myeloproliferative disorders, and certain variants may show features of both (see Figure 71-1). In the chronic myeloproliferative disorders, patients present with erythrocytosis, thrombocytosis, or leukocytosis (or some combination). In contrast, in myelodysplastic syndromes, patients present with significant dyshematopoiesis and intramedullary apoptosis, resulting in ineffective hematopoiesis and peripheral pancytopenia (see Table 71-1).