Thrombocytosis versus thrombocythemia - differentiation of an elevated platelet count

Differentiation of an elevated, repeatedly determined platelet count (great er than or equal to 500x10(9)/l) includes the discrimination between reacti ve causes generated by a variety of underlying conditions and a neoplastic myeloproliferative disorder (CMPD). In addition to clinical findings, the e volution of laboratory data during follow-up and histology of the bone marr ow exerts a significant diagnostic impact. Characteristic features are not only expressed by hematopoiesis, but also by the myeloid stromal compartmen t. White the megakaryocyte-rich subtype of chronic myeloid leukemia (CML) a nd the 5q(-) syndrome (MDS) are dominated by abnormal micromegakaryocytes, in polycythemia vera [PV) this cell lineage reveals a pleomorphous appearan ce. In essential thrombocythemia (ET), a prevalence of giant megakaryocytes with deeply lobulated [staghorn-like] nuclei may be encountered. A clear-c ut discrimination of ET from early (hypercellular) stages of idiopathic (pr imary) myelofibrosis (IMF) presenting with thrombocythemia becomes possible , provided the conspicuous atypical features of megakaryopoiesis characteri zing the latter entity are taken into account. Moreover, CML displays a pre dominance of the granulocytic lineage whereas PV shows a panmyelosis or tri lineage proliferation, involving erythropoiesis, in particular. In contrast , erythropoiesis is markedly reduced in CML and to a lesser degree also in IMF. In CMPDs extreme values of iron deposits may be found, ranging from a total lack (PV) to minor amounts (CML] and a normal staining reaction (ET). Similar results are exhibited regarding reticulin fibrosis, which is usual ly not present in ET, rarely observed in PV and detectable to a variable de gree in CML and IMF.