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=1766057348&Signature=rD9Bgm4hT02O7kEYmmuRhOMODob9vKDAPmXRdNFVd7lY9Gw3GpmxBdRdKUHlSa1gkPhtwYOEpAhfcabzW-YeQBEgK3Ygwez4mzi96G8T57AecESdeym6DkPgfdhzDXWAhJRM6BB~Sp9uAgdfalFZaLJP0glwkeIGyMCrAxNZLDL6hFn4WUYFaWs3VzqWn3Cpi62Gv6-91uj0O7UxpeVl1TW7tOYH2iFTN4E3KL6gGWQchfDL4-pPMfgAdEVwAnaN4CCtF6H0ty8XxAzLnreO2ww4VUKILzn6lDYHF47Z8KZGQCV6-MS2PtQJ-f2UoUmh4yWaqzDwh5eqseSRm2jwYA__&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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