Large intramuscular hematoma due to acquired Factor VIII inhibitors in post Polycythemia Vera-Myelofibrosis.

A 59-year-old man with Janus kinase-2 (JAK2) V617F mutation-positive polycythemia vera, evolving to myelofibrosis presented with a right thigh hematoma. Further evaluation showed prolonged activated partial thromboplastin time (aPTT), which was partially corrected after mixing with pooled normal plasma (PNP) and, low factor VIII (F VIII) levels. He was diagnosed to have acquired F VIII inhibitors, and treated with prednisolone for inhibitor eradication. After four weeks of treatment, his aPTT normalized, F VIII rose to 86% and the hematoma was resolved. The case report is followed by a discussion on the topic, revisiting the handful of cases published so far, and the possible mechanisms leading to inhibitor formation in MPN. Further studies are required to elucidate the pathophysiology and the incidence of F VIII inhibitor development in myeloproliferative neoplasms.