Latent myeloproliferative disorder revealed by the JAK2-V617F mutation and endogenous megakaryocytic colonies in patients with splanchnic vein thrombosis

Splanchnic vein thrombosis (SVT), a complication of myeloproliferative disorders (MPDs), sometimes reveals polycythemia vera (PV) or essential thrombocythemia (ET).¹  However, polycythemia and thrombocytosis may be masked by hemodilution and/or hypersplenism in SVT patients, making the diagnosis of MPD difficult. In this retrospective study, SVT was diagnosed by Doppler ultrasound and/or multidetector spiral computed tomography for 45 patients with normal or low hematocrit and platelet counts. These patients were examined for the presence of 2 clonal markers specific for MPDs: the JAK2-V617F mutation²  and the capacity to form endogenous erythroid colonies (EECs) and/or endogenous megakaryocytic colonies (EMCs), observed in both mutated and nonmutated MPDs (Table 1).^3-5  Levels of expression of JAK2 wild-type (WT) or mutated (V617F) were determined in blood granulocytes (37 patients) and/or in May-Grünwald-Giemsa–stained myeloid colonies (11 patients for whom granulocytes were not available) using allele-specific quantitative polymerase chain reactions (PCRs) adapted to complementary (granulocytes) or genomic (colonies) DNA.^5,6  Formation of EECs/EMCs by bone marrow (BM) progenitors in collagen gels, serum erythropoietin, and granulocyte PRV-1 levels were also analyzed.^3-5,7 

JAK2-V617F was detected in granulocytes from 12 of 37 SVT patients and in myeloid colonies from 2 of 8 additional patients; EMCs were observed for 14 patients (2 also formed EECs; Figure 1). Altogether, 14 (31%) of 45 SVT patients carried the JAK2-V617F mutation and 17 (38%) of 45 were positive for JAK2-V617F and/or EMCs/EECs, and were therefore considered to be suffering latent MPD. Two patients without EMCs were positive for JAK2-V617F, and 3 patients negative for JAK2-V617F had EMCs. BM histology, which was not always performed during anticoagulant treatment, was available for 22 patients and in favor of MPDs⁸  (2 PV, 9 ET) for 11 of 12 patients with latent MPDs (JAK2-V617F and/or EMCs/EECs); 1 of 2 patients with only EMCs rapidly developed typical ET. Histologic features of MPD were not observed in 10 of 10 SVT patients negative for both EMCs/EECs and the JAK2 mutation (Figure 1). In addition, a low serum erythropoietin level (< 3.3 IU/L) was found only in MPD patients,⁷  and 7 of 9 patients with high PRV-1 levels carried the JAK2-V617F mutation, an expected finding since PRV-1 expression correlates with JAK2 activation.⁹  Consistent with our previous observation of JAK2 overexpression in reactive states,⁵  the quantification of total JAK2 transcripts revealed that granulocytes of SVT patients expressed high levels of JAK2 whether they suffer from MPDs or not (Table 1). Importantly, the proportion of mutated JAK2 was typically low (median, 18%; range, 2%-51%), close to the values found in ET.⁵  Among the 3 patients with more than 40% JAK2-V617F, 1 had EECs and the other 2 had low erythropoietin levels; 2 later developed PV. Finally, acquired thrombophilia was found in 8 of 28 patients without MPDs but never in MPD patients; association with inherited thrombophilia was equally frequent in both groups of patients (Table 1; Figure 1).

In conclusion, detection of JAK2-V617F and EECs/EMCs, which can be performed during anticoagulant treatment, diagnosed a latent MPD, most often ET, in 38% of patients with SVT and normal/low blood cell counts. We propose that at least the presence of JAK2-V617F in blood granulocytes should be systematically investigated in such situations.