Splenectomy unveils thrombocytosis in underlying myeloproliferative neoplasms with extrahepatic portal vein obstruction.

Extrahepatic portal vein obstruction (EHPVO) is a rare disease with myeloproliferative neoplasm (MPN) as the most common cause. We report that hypersplenic hematologic changes in EHPVO might be eliminated by MPN. Through experience with splenectomy for variceal control with EHPVO, we suspected that spleen might mask MPN-induced thrombocytosis, and that MPN might have a significant influence on excessive thrombocytosis after splenectomy. To clarify the influence of MPN and spleen on platelet trends, we conducted a retrospective hospital database analysis, evaluating 8 EHPVO patients with splenectomy (2 males, 6 females; from 17 years to 64 years, mean 38.3 years). Three (37.5%) of 8 were diagnosed as MPN by JAK2V617F mutation. The perioperative serum platelet counts in EHPVO without MPN were 10.5, 35.4, and 36.6 (x10⁴/μL) preoperatively, after 1 week and 3 weeks, respectively. The platelet counts in EHPVO with MPN were 34.2, 86.4, and 137.0 (x10⁴/μL), respectively. Splenectomy and MPN showed positive interaction on platelet increasing with statistical significance. We also examined the spleen volume index (SpVI: splenic volume (cm³) / body surface area (m²) and postoperative platelet elevations ratio (PER: 3-week postoperative platelet counts / preoperative platelet counts). However, both SpVI and PER showed no significant difference with or without MPN. Histological examination revealed splenic congestion in all 8 EHPVO cases, and splenic extramedullary hematopoiesis in 2 of 3 MPN. In EHPVO with MPN, hypersplenism causes feigned normalization of platelet count by masking MPN-induced thrombocytosis; however, splenectomy unveils postoperative thrombocytosis. Spleen in EHPVO with MPN also participates in extramedullary hematopoiesis.