Aberrant proplatelet formation in chronic myeloproliferative neoplasms.

Proplatelets represent pseudopodia of megakaryocytes which extend into bone marrow sinuses to release platelets. Proplatelets were visualized by immunohistochemical and confocal microscopy. In trephines from essential thrombocythaemia (ET, n=10), fibrotic (n=10) and pre-fibrotic (n=10) primary myelofibrosis (PMF) there was a significant increase of proplatelet density compared with normal bone marrow samples (n=10; p<0.001). Manifest fibrosis exhibited the highest density and volume ratio with significant differences to non-fibrotic PMF (p<0.001) and ET (p<0.001). This study demonstrates that besides megakaryocytic proliferation extensive pseudopodial proplatelet formation provides a hallmark of MPN. Fibrosing differ from non-fibrosing MPN by density and size of aberrant proplatelets.