A 44-year old female with unremarkable past clinical history refers to the Hematology Clinic for persistent thrombocytosis (Hb = 15.2 g/dL; Hct = 44.8%; WBC = 12.65 × 109/L [N = 9.58 × 109/L]; Plt = 742 × 109/L). Epo levels are close to the lower limit of normal (4.29 mU/mL; range: 4.3–29), LDH is not increased (206 U/L, range: 135–214) and JAK2 mutation is detected (VAF = 5.5%). Splenomegaly is not documented at clinical examination and sonography. BM biopsy (d–f) discloses a hypercellular marrow with features of panmyelosis, maturing erythroid and myeloid lineages and polymorphous, and loosely clustering megakaryocytes with frequent giant hyperlobated forms. A minor increase in reticulin fibers is observed, consistent with MF-1 according to WHO criteria. This case displays borderline features between a pre-polycythemic phase of PV (highly supported by the very typical morphologic pattern) and pre-fibrotic PMF.\nA diagnosis of ET is ruled out by BM histology. In contrast to case 1, the still low JAK2 allele burden could be responsible for the blood count, which is not fully consistent with PV. In similar cases, concurrent hematopoiesis-modifying factors (e.g., thalassemic trait, vitamin deficiencies, malabsorption, etc.) should be investigated. In addition, a minor increase in fibrosis should warrant closer monitoring.
A 79-year old woman with beta-thalassemia minor and IgG+ monoclonal gammopathy of undetermined potential presents with stable Hb levels and a steady increase of platelet count (Hb = 13.2 g/dL; Hct = 43.5%; WBC = 14.2 × 109/L [N 9.67]; Plt = 866 × 109/L; LDH levels within normal ranges, Epo not assessed). JAK2 mutation is detected on peripheral blood (VAF not known). A BM biopsy (g–i) is hypercellular, with erythroid precursor expansion, megaloblastosis, and clustering of megakaryocytes, ranging in morphology from small, hypolobulated forms (including naked nuclei) to giant, hyperlobulated (“staghorn”) cells. No increase in reticulin fibers and CD34+ blasts is observed; the lympho-plasmacytic infiltrate is unremarkable.\nThe global picture strongly favors a diagnosis of MPN, but the differential diagnosis between ET and PV cannot be definitively settled. The former is favored by thrombocytosis and by prominent ET-type megakaryocyte morphology, and the latter is supported by the coexistence of neutrophilia alongside with normal Hb levels (possible effect of the concurrent thalassemic trait) [].