Diagnostic impact of bone marrow histopathology in polycythemia vera (PV)

The criteria of the Polycythemia Vera Study Group (PVSG), although acknowledged as the gold standard to establish the diagnosis of polycythemia vera (PV), do not regard bone marrow (BM) histopathology. Arguments include the existence of sufficient objective markers of disease and the lack of independently performed morphological studies or standardized criteria. The aim of this review is to evaluate morphological characteristics of erythrocytosis and to determine whether distinctive patterns of histopathology exist. A review of the pertinent literature and evaluation of 334 patients from our files with a borderline to marked increase in hemoglobin was performed. In extension to former descriptions of BM features by the PVSG, a tri-lineage myeloproliferation (panmyelosis) with a pleomorphous appearance of megakaryopoiesis revealed that, besides increase in size, there was a lack of gross cytological anomalies. Differentiation from secondary polycythemia (SP) was accomplished by regarding these features and the conspicuously expressed stromal changes (plasmacytosis, eosinophils, cell debris and iron deposits). In about 96% of this cohort a clear-cut separation from SP was achieved, even in the initial (latent) stages. When accompanied by an elevated platelet count, these precursor stages may clinically mimick essential thrombocythemia because they are not recognized by the conventional criteria. Advanced stages (spent phases) of PV were consistent with an increased left-shifted granulocytic proliferation, accompanied by reduction of erythroid precursors and progressive myelofibrosis (post-polycythemic myeloid metaplasia). Finally, an increase in dysplastic changes and immaturity signalled a transition into blastic crisis. In conclusion, PV is characterized by a distinctive pattern of histopathology that has been gained in an independent and blind fashion and therefore, dissolves arguments about failing specificity.