γ-Glutamyl Transferase Is an Independent Biomarker of Splanchnic Thrombosis in Patients With Myeloproliferative Neoplasm

Thrombosis at Unusual Sites: Focus on Myeloproliferative Neoplasms and Paroxysmal Nocturnal Hemoglobinuria

Patients with thrombosis at an unusual site will need to be explored for rare causes of thrombosis. Two of these rare causes include myeloproliferative neoplasms (MPNs) and paroxysmal nocturnal hemoglobinuria (PNH). It is important not to overlook these causes, since they require specific management, in addition to antithrombotic treatment (anticoagulants, antiplatelet agents). Unusual sites of venous thrombosis include upper extremity veins, splanchnic veins, cerebral veins, and retinal veins, and unusual sites of arterial thrombosis include renal, adrenal, splenic and mesenteric arteries, and intracardiac and aortal locations. Suspicion for MPN and PNH should be raised if there are concomitant abnormalities, such as elevated or decreased blood cell counts or splenomegaly. Diagnosis of MPN and PNH should include JAK2V617F mutational screening as well as flow cytometric assessment of GPI-anchored proteins in the peripheral blood, respectively. Specific treatments for MPN may include phlebotomy or cytoreductive drugs such as hydroxyurea, anagrelide, pegylated interferon-alpha, or Janus kinase inhibitors. Drugs used for PNH treatment include terminal complement inhibitors, such as eculizumab and ravulizumab, as well as proximally acting inhibitors such as pegcetacoplan or iptacopan. Patients with MPN and PNH are at high risk for thrombosis during their entire lifetime and should thus be followed by specialists experienced in the care of these diseases.

Splanchnic Vein Thrombosis in Myelofibrosis-An Underappreciated Hallmark of Disease Phenotype

Splanchnic vein thrombosis (SVT) encompasses thrombosis in the vessels of the splanchnic basin and has a relatively rare occurrence with a reported frequency in the general population of 1-2%. An episode of seemingly unprovoked SVT almost always triggers a diagnostic work-up for a Philadelphia chromosome-negative myeloproliferative neoplasm (MPN), since atypical site thrombosis is a hallmark of MPN-associated thrombophilia. Primary myelofibrosis (PMF) is a rare MPN with an estimated incidence between 0.1 and 1/100,000 per year. Although prothrombotic tendency in PMF is not envisioned as a subject of specific therapeutic management, unlike other MPNs, such as polycythemia vera (PV) and essential thrombocythemia (ET), thrombotic risk and SVT prevalence in PMF may be comparably high. Additionally, unlike PV and ET, SVT development in PMF may depend more on procoagulant mechanisms involving endothelium than on blood cell activation. Emerging results from registry data also suggest that PMF patients with SVT may exhibit lower risk and better prognosis, thus highlighting the need for better thrombotic risk stratification and identifying a subset of patients with potential benefit from antithrombotic prophylaxis. This review highlights specific epidemiological, pathogenetic, and clinical features pertinent to SVT in myelofibrosis.

Prevalence of CALR mutations in splanchnic vein thrombosis: A systematic review and meta-analysis

BACKGROUND

The prevalence of calreticulin (CALR) mutations in splanchnic vein thrombosis (SVT) varies among studies. The role of routine screening for CALR mutations in SVT patients remains a debate.

AIM

To synthesize the prevalence of CALR mutations according to the different types (i.e., Budd-Chiari syndrome [BCS] and portal vein thrombosis [PVT]) and characteristics (i.e., with and without myeloproliferative neoplasms [MPNs] and JAK2V617F mutation) of SVT patients.

METHODS

Eligible studies were searched by the PubMed and Embase databases. The study quality was assessed according to the STROBE checklist. The proportion of CALR mutations was pooled by using a random-effects model. The heterogeneity and publication bias were calculated.

RESULTS

Eleven papers were included. The study quality was moderate to high. The pooled proportion of CALR mutations was 1.21%, 1.41%, and 1.59% in SVT, BCS, and PVT patients, respectively; 1.52%, 1.03%, and 1.82% in these patients without JAK2V617F mutation, respectively; 3.71%, 2.79%, and 7.87% in these patients with MPN, respectively; and 15.16%, 17.22%, and 31.44% in these patients with MPN but without JAK2V617F mutation, respectively. Only the meta-analysis examining the prevalence of CLAR mutations in BCS patients with MPN but without the JAK2V617F mutation showed statistically significant heterogeneity. Statistically significant publication bias was seen only in the meta-analysis examining the prevalence of CALR mutations in SVT patients without the JAK2V617F mutation.

CONCLUSION

Screening for CALR mutations may have a role in SVT patients with a high probability of MPN in whom the JAK2V617F mutation has been excluded.

Elevated plasma levels of procoagulant microparticles are a novel risk factor for thrombosis in patients with myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs), including polycythemia vera and essential thrombocythemia, are frequently associated with thrombotic complications. Prevention of thrombotic events is thus a primary aim of the current treatment for these disorders. Although it is known that microparticles (MPs), which are small vesicles released from cell membranes and circulate in the blood, directly contribute to thrombosis via their procoagulant activity, potential associations between plasma levels of MPs and the risk of thrombotic events in MPNs have not been reported. In the present study, we characterized plasma levels of MPs and assessed their potential association with the occurrence of thrombotic events in 59 patients with MPNs. Plasma levels of procoagulant MPs expressing tissue factor (TF+ MPs) were significantly higher in patients suffering thrombotic events than in patients without such events (median/μl plasma: 33.8 vs 47.2, p = 0.02). Among patients who developed thrombotic events, irrespective of patients' blood counts, TF+ MP were significantly higher in patients without cytoreductive therapy than in those receiving cytoreductive therapy (101.2 vs. 42.5, p < 0.001). These results suggest that elevated levels of TF+ MP may be considered as a novel surrogate marker for thrombotic events in MPN patients. Further studies are needed to clarify the mechanism involved.