Essential thrombocythaemia (ET)

This picture of peripheral blood smear shows clumps of many platelets by thrombocytosis and two segmented neutrophils.

The marrow aspirate smear is normocellular, with a marked proliferation of megakaryocytes, which are large to giant, have abundant, mature and granular cytoplasm, deeply lobulated or hyperlobulated nuclei, and form loose clusters. Naked nuclei of megakaryocytes are marked by green arrows.

In this picture of marrow aspirate smear with two giant megakaryocytes, the upper cell has typical hyperlobulated (stag-horn shape) nuclei and some nuclear fragments in the cytoplasm.

A. The scheme shows domains of the wild-type calreticulin protein (N, P, C; SP – signal peptide).

B. Calreticulin mutations involve insertions or deletions in exon 9, leading to the creation of a new C-end of the protein (red arrow). Due to the loss of KDEL sequence, the protein is no longer kept in the endoplasmic reticulum.

This figure shows PCR amplification products. The first band shows a CALR-negative sample (lane 2, yellow arrow), whereas the second and third sample are CALR-positive. One mutation is of type 1 – deletion of 52 bp (lane 3, red arrow A) and one mutation is of type 2 – insertion of 5 bp (lane 4, red arrow B). The green arrow (lane 5) indicates no template control (NTC). A DNA size marker was applied (lane 1, black arrow).

Essential thrombocythaemia. 50-year old man, thrombocytosis 587×10⁹/L. Normocellular haematopoiesis without fibrosis.

Bone marrow trephine biopsy, haematoxylin and eosin stain.

Essential thrombocythaemia. 50-year old man, thrombocytosis 587×10⁹/L. Increased number of megakaryocytes in otherwise normocellular haematopoiesis with an adequate appearance of the granulocytic and erythroid series.

Bone marrow trephine biopsy, haematoxylin and eosin stain.

Essential thrombocythaemia. 50-year old man, thrombocytosis 587×10⁹/L. Megakaryocytes are forming loose clusters. The cells are normally sized or enlarged, mature appearing, often with hyperlobated nuclei.

Bone marrow trephine biopsy, haematoxylin and eosin stain.