The term myeloproliferative disorders (MPDs) describes a group of conditions in which an intrinsic stem cell defect is present in the bone marrow. This leads to hypercellularity in one or more of the myeloid cell lines (red blood cells, platelets, granulocytes and their precursors), or increased bone marrow fibrosis. MPDs are rare; combined annual incidence is 6 per 100,000.
MPDs may present in asymptomatic patients as an incidental finding, or may be associated with constitutional features such as weight loss, sweats or lethargy. Splenomegaly is common but lymphadenopathy is not a feature. The most significant complications are: arterial thrombosis, venous thrombosis, secondary marrow fibrosis and transformation to acute myeloblastic leukaemia (AML). Treatment aims to reduce the risk of such complications.
Recent advances in the understanding of the pathogenesis of these disorders have radically changed the approach to the diagnosis of MPD and are the focus of new treatment developments.