Volumetric splenomegaly in patients with essential thrombocythemia and prefibrotic/early primary myelofibrosis.

Non-palpable, volumetric splenomegaly at diagnosis was evaluated using computed tomography in patients with essential thrombocythemia (ET) and prefibrotic/early primary myelofibrosis (pre-PMF) based on 2016 World Health Organization guidelines. Each patient's spleen volume was adjusted for their age and body surface area. The degree of splenomegaly was classified as no, borderline volumetric, overt volumetric, or palpable splenomegaly. Seventy-six patients with ET (median age, 62.5 years) and 19 patients with pre-PMF (median age, 65 years) were followed up for a median of 2.4 years (range 0.1-17.6 years) and 4.2 years (range 0.2-19.6 years), respectively. Spleen volume was significantly greater in pre-PMF patients than in ET patients (377.9 ± 92.2 cm3 vs. 224.9 ± 115.2 cm3, P < 0.001). No, borderline volumetric, overt volumetric, and palpable splenomegaly were found in 42 (55.3%), 24 (31.6%), 10 (13.2%), and 0 (0%) patients with ET, respectively, and in 0 (0%), 8 (42.1%), 19 (52.6%), and 1 (5.2%) patient with pre-PMF, respectively (P < 0.001). Volumetric splenomegaly did not affect thrombosis-free survival in patients with ET or those with pre-PMF. This study indicates that all patients with pre-PMF present with splenomegaly, whereas half of the patients with ET have a normal-sized spleen at diagnosis.