https://orcid.org/0000-0002-9937-4306
![A 75-year-old man diagnosed with JAK2+ myelodysplastic/myeloproliferative neoplasm, unclassifiable (MDS/MPN-U), presented with extreme thrombocytosis of 2118 × 109/L. Myeloid hyperplasia and increased and frequently clustered hypolobulated megakaryocytes were observed on bone marrow trephine (panel A arrows; hematoxylin and eosin [H&E] stain; original magnification ×20) and aspirate (panel B arrows; Wright-Giemsa stain; original magnification ×40). Thrombocytosis was controlled with hydroxyurea and, for the last 3 months, with ruxolitinib. Two years after diagnosis, he developed rapidly progressive neutrophilia. His leukocyte count increased from 36.8 × 109/L to 260.1 × 109/L in 19 days; hemoglobin was 8.2 g/dL, and platelet count was 251 × 109/L. The peripheral blood film showed increased granulocytes, frequently dysplastic (panel C arrows; Wright-Giemsa stain; original magnification ×60), without increased monocytes or blasts. Bone marrow trephine showed marked myeloid hyperplasia (panel D; H&E stain; original magnification ×10), without fibrosis or increased blasts. His karyotype was 46XY. Next-generation sequencing detected the following mutations: JAK2 p.Val617Phe, ASXL1 p.Glu635ArgfsTer15, TET2 p.Pro656ThrfsTer25, and EZH2 p.Cys548Arg, with respective allele burdens of 36%, 50%, 47%, and 98%. He subsequently developed multiorgan failure as a result of leukostasis. Hydroxyurea was restarted, and leukapheresis was attempted, but we were unable to control progressive leukocytosis. The patient died within 5 days.](https://ash.silverchair-cdn.com/ash/content_public/journal/blood/134/23/10.1182_blood.2019002559/7/m_bloodbld2019002559f1.png?Expires=1769718790&Signature=irPnsb6Sdp3S0pzqlDPig4I~u-ahUm-e3acn3uwz~KkZbYb0UeLpRDLbMmUa~nOnb562uvFyUSsVl4I0JZ1lHj8hwJ4fWm8jvu6PQSt4xC7Xm2bhl33EUF2xYgk9av2qcSBhUnnLR3-mZy6Wp-k3BiZGdgOmyCM-IB-NPrOfBD99~IAfQuIhBo1rV67fO6qzP8pemFGRhr8uEuoWW5~NC3zcgpOONtvZvBrQ~Hnet-nhmU9GG00UH~RxoFhULDZ-U1CZwLeFWePym3BPxQ5sRru7H9iQClxKjjXqKnQ2Xh3VnPDy7rlsSCFWMkXVK~LzME-XeCkqewrsLOIyRVKrXg__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
A 75-year-old man diagnosed with JAK2+ myelodysplastic/myeloproliferative neoplasm, unclassifiable (MDS/MPN-U), presented with extreme thrombocytosis of 2118 × 109/L. Myeloid hyperplasia and increased and frequently clustered hypolobulated megakaryocytes were observed on bone marrow trephine (panel A arrows; hematoxylin and eosin [H&E] stain; original magnification ×20) and aspirate (panel B arrows; Wright-Giemsa stain; original magnification ×40). Thrombocytosis was controlled with hydroxyurea and, for the last 3 months, with ruxolitinib. Two years after diagnosis, he developed rapidly progressive neutrophilia. His leukocyte count increased from 36.8 × 109/L to 260.1 × 109/L in 19 days; hemoglobin was 8.2 g/dL, and platelet count was 251 × 109/L. The peripheral blood film showed increased granulocytes, frequently dysplastic (panel C arrows; Wright-Giemsa stain; original magnification ×60), without increased monocytes or blasts. Bone marrow trephine showed marked myeloid hyperplasia (panel D; H&E stain; original magnification ×10), without fibrosis or increased blasts. His karyotype was 46XY. Next-generation sequencing detected the following mutations: JAK2 p.Val617Phe, ASXL1 p.Glu635ArgfsTer15, TET2 p.Pro656ThrfsTer25, and EZH2 p.Cys548Arg, with respective allele burdens of 36%, 50%, 47%, and 98%. He subsequently developed multiorgan failure as a result of leukostasis. Hydroxyurea was restarted, and leukapheresis was attempted, but we were unable to control progressive leukocytosis. The patient died within 5 days.
Dysplasia is a distinguishing feature of MDS/MPN-U, usually absent in myeloproliferative disorders; however, rapidly progressive granulocytosis and leukostasis are extremely rare.
A 75-year-old man diagnosed with JAK2+ myelodysplastic/myeloproliferative neoplasm, unclassifiable (MDS/MPN-U), presented with extreme thrombocytosis of 2118 × 109/L. Myeloid hyperplasia and increased and frequently clustered hypolobulated megakaryocytes were observed on bone marrow trephine (panel A arrows; hematoxylin and eosin [H&E] stain; original magnification ×20) and aspirate (panel B arrows; Wright-Giemsa stain; original magnification ×40). Thrombocytosis was controlled with hydroxyurea and, for the last 3 months, with ruxolitinib. Two years after diagnosis, he developed rapidly progressive neutrophilia. His leukocyte count increased from 36.8 × 109/L to 260.1 × 109/L in 19 days; hemoglobin was 8.2 g/dL, and platelet count was 251 × 109/L. The peripheral blood film showed increased granulocytes, frequently dysplastic (panel C arrows; Wright-Giemsa stain; original magnification ×60), without increased monocytes or blasts. Bone marrow trephine showed marked myeloid hyperplasia (panel D; H&E stain; original magnification ×10), without fibrosis or increased blasts. His karyotype was 46XY. Next-generation sequencing detected the following mutations: JAK2 p.Val617Phe, ASXL1 p.Glu635ArgfsTer15, TET2 p.Pro656ThrfsTer25, and EZH2 p.Cys548Arg, with respective allele burdens of 36%, 50%, 47%, and 98%. He subsequently developed multiorgan failure as a result of leukostasis. Hydroxyurea was restarted, and leukapheresis was attempted, but we were unable to control progressive leukocytosis. The patient died within 5 days.
Dysplasia is a distinguishing feature of MDS/MPN-U, usually absent in myeloproliferative disorders; however, rapidly progressive granulocytosis and leukostasis are extremely rare.
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![A 75-year-old man diagnosed with JAK2+ myelodysplastic/myeloproliferative neoplasm, unclassifiable (MDS/MPN-U), presented with extreme thrombocytosis of 2118 × 109/L. Myeloid hyperplasia and increased and frequently clustered hypolobulated megakaryocytes were observed on bone marrow trephine (panel A arrows; hematoxylin and eosin [H&E] stain; original magnification ×20) and aspirate (panel B arrows; Wright-Giemsa stain; original magnification ×40). Thrombocytosis was controlled with hydroxyurea and, for the last 3 months, with ruxolitinib. Two years after diagnosis, he developed rapidly progressive neutrophilia. His leukocyte count increased from 36.8 × 109/L to 260.1 × 109/L in 19 days; hemoglobin was 8.2 g/dL, and platelet count was 251 × 109/L. The peripheral blood film showed increased granulocytes, frequently dysplastic (panel C arrows; Wright-Giemsa stain; original magnification ×60), without increased monocytes or blasts. Bone marrow trephine showed marked myeloid hyperplasia (panel D; H&E stain; original magnification ×10), without fibrosis or increased blasts. His karyotype was 46XY. Next-generation sequencing detected the following mutations: JAK2 p.Val617Phe, ASXL1 p.Glu635ArgfsTer15, TET2 p.Pro656ThrfsTer25, and EZH2 p.Cys548Arg, with respective allele burdens of 36%, 50%, 47%, and 98%. He subsequently developed multiorgan failure as a result of leukostasis. Hydroxyurea was restarted, and leukapheresis was attempted, but we were unable to control progressive leukocytosis. The patient died within 5 days.](https://ash.silverchair-cdn.com/ash/content_public/journal/blood/134/23/10.1182_blood.2019002559/7/m_bloodbld2019002559f1.png?Expires=1769718791&Signature=2yfJh61Do~cFWq4iUpsOseAOx8c59xdn9uE4DbURjSofu6O5hfZAYcgMcCHUTrz3v4tW0DfBJzoEqDa300oJidDM6kQyuCjS0P~W6FkB0uR4RIDVERp250GRPoIFU~5718hUFpT6~ZUEIuBFeSZdGgUK1lrDSGR~ma~g1z28YWYdwdAKuBWV6BF8fGPKBXoTX9Ya44qRJadD7os-m6m~NOOoCjNOWiQS7lW8HF6csl-26d2BjChgEukGY0iFj2E7DVIgp~o1BpiQMaIAiQfsXhKOM078~Tqi7eY8kvYIEROWXYQoDJqNViYEE-I-dILcn8InbHRpcr8FqRIm5Wz-7A__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
