Frequency and Determinants of Thrombotic and Bleeding Complications in Ph Negative Myeloproliferative Neoplasms (MPN): The Role of Adamts-13 and VWF Activities in an Italian Cohort 0f 88 Well Characterized Patients

Patients with Ph-negative Myeloproliferative Neoplasms (MPN) such as Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF) can be exposed during the course of these MPN to thrombotic and bleeding complications, with increased morbidity and mortality. Age, previous history of thrombosis, increased White Blood Cell (WBC) and Jak2 allele burden have been proposed as risk factors for Venous (VTE) and Arterial (ATE) thromboses while bleeding has been previously associated with abnormalities of the von Willebrand factor (VWF).

To investigate any significant role of ADAMTS-13 and VWF activities in the thrombotic and bleeding complications observed in a small but well characterized cohort of MPN patients.

88 consecutive patients were diagnosed at the Hematology and Transfusion Medicine Division, L.SACCO University Hospital of Milan, according to WHO criteria. Patients signed an informed consent to participate in this clinical study with a protocol approved by local IRB and they showed MPN type (%), mean age (range), gender M/F and Jak2 positivity (%) as follows: PV[n=42 (48%), 68 (36–86), 18/24; 85.7%]; ET [n=34 (38%), 66 (30–93), 10/24, 61.7%]; PMF [n=12 (14%), 67 (37–88), 7/5, 58%]. Thrombotic and bleeding episodes were recorded and managed from the time of diagnosis and associated with the use of aspirin (ASA) and of other MPN therapies. Among additional lab parameters, plasmatic ADAMTS-13 and VWF activities were also measured at enrolment as endothelial/platelet marker. These activities were assayed with Technozym ADAMTS-13 activity (Technoclone GmbH, Austria), Innovance VWF-GPIb activity (Siemens AG, Germany) and HemosIL-VWF antigen (Instrumentation Laboratory, USA). Multimeric analyses were also tested using very sensitive intermediate SDS-agarose gel electrophoresis. Statistical analyses were performed by SPSS-17.2.

59/88 (67%) patients did not show any thrombotic or bleeding complications during the 6-year follow-up. In these cases mean (range) values of VWF:GPIb and VWF:Ag were 104 (29–202) and 133 (52–288) U/dL while ADAMTS-13 was 102 (63–143). 20/88 (23%) cases showed at least one thrombotic event (13ATE/7VTE): AMI (6), STROKE (6), TIA (2), PE (1), DVT (7). Patients with thromboses showed relatively higher values VWF:GPIb and lower ADAMTS-13 and this was confirmed in multivariate analysis especially for ET [VWF:GPIb=135 (61–237) U/dL, p=0.004 and ADAMTS-13=89(62–134), p=0.009]. Major bleeding episodes mainly mucosal (5 gastrointestinal, 3 post-surgery, 1 severe menorrhagia) requiring blood transfusions or hysterectomy were observed in 9/88 (10%) patients. At the multivariate analysis, major bleedings were significantly associated with lower VWF:GPIb [68 (25–111) U/dL, p=0.022), lower VWF:Ag [93 (35–146) U/dL, p=0.016] and to the ASA intake (p=0.006). Most of these bleeders showed also a relative loss of the highest molecular weight multimers.

Based on these observations, we confirm that thrombotic events in MPN may certainly have multiple risk factors: however, lower ADAMTS-13 and higher VWF activities might play a role as additional risk factors especially in ET. Conversely, lower levels of VWF with loss of the largest multimers are important risk factors for bleeding in MPN especially in patients treated with ASA.

No relevant conflicts of interest to declare.