Idiopathic erythrocytosis--a declining entity

Idiopathic erythrocytosis: A diagnostic and management challenge with emerging areas for exploration

Despite published algorithms for approaching the work-up of erythrocytosis, a significant proportion of patients are left with uncertainty as to its aetiology and prognosis. The term 'idiopathic erythrocytosis' (IE) is applied when known primary and secondary aetiologies have been ruled out. However, the assignment of secondary aetiologies is not always straightforward or evidence based, which can lead to misdiagnosis and heterogeneity in cohort studies. Furthermore, new studies have identified germline or somatic mutations that may affect prognosis. Epidemiological and cohort data are inconsistent as to whether IE increases the risk for complications such as arterial and venous thromboembolism, clonal transformation or comorbid conditions. Randomized trials assessing the role of phlebotomy for long-term management of IE have not been performed, so treatment remains a vexing problem for clinicians. Standardization of terminology and testing strategies, including comprehensive genetic screening in clinical research, are key to refining our understanding of IE.

Blood p50 evaluation enhances diagnostic definition of isolated erythrocytosis

BACKGROUND

High oxygen-affinity haemoglobin variants and 2,3-diphosphoglycerate (2,3-DPG) deficiency are inherited diseases generating low tissue oxygen tension and erythropoietin-driven erythrocytosis, that characterizes the clinical phenotype of patients. Level of blood p50 (the oxygen tension at which haemoglobin is 50% saturated) is used to recognize these conditions.

OBJECTIVES

To define the clinical utility of blood p50 measurement in the diagnosis of isolated erythrocytosis.

SUBJECTS AND DESIGN

Venous blood p50 measurement was included in the diagnostic work-up of 102 consecutive patients with isolated erythrocytosis besides blood cell count, arterial oxygen saturation, serum erythropoietin measurement and screening for JAK2 mutations.

SETTING

Haematological Outpatient Section at University Hospital.

RESULTS

Seven patients had relative erythrocytosis. Among 95 patients with absolute erythrocytosis, 4 (4.2%) had decreased p50 level. The extended study of family members revealed a familial inheritance. Two families had haemoglobin variants already described as Haemoglobin Malmö and Haemoglobin San Diego. In one family, the proband had a new high oxygen-affinity haemoglobin variant (Haemoglobin Safi) resulting from the transversion C-->A at codon 81 of the alpha2-globin gene. In the last family, a deficiency of 2,3-DPG was found. Within the 91 patients with normal p50 values, 46 (51%) had secondary erythrocytosis, 13 (14%) polycythemia vera and 32 (35%) idiopathic erythrocytosis.

CONCLUSIONS

This study suggests that the investigation of blood p50 level may be useful to define diagnosis in patients with isolated erythrocytosis.

JAK2 V617F mutation is rare in idiopathic erythrocytosis: a difference from polycythemia vera

A single mutation 1849G>T in the JAK2 gene (V617F) has recently been described in classical myeloproliferative disorders (MPD). To investigate the incidence and clinical significance of the JAK2 mutation, we performed allele-specific polymerase chain reaction (PCR) and enzyme-based assessment in 11 idiopathic erythrocytosis (IE) and 15 polycythemia vera (PV) patients. Aberrant bands indicating the V617F mutation were detected in only one of 11 patients with IE, whereas all of the 15 patients with PV showed the JAK2 mutation. Sequence analysis was subsequently performed in the IE patient showing aberrant bands on allele-specific PCR, and a nucleotide change corresponding to the V617F mutation was detected in four of 29 clones tested. This patient might have progressed to PV according to the new WHO diagnostic criteria proposed in 2007, since a gradual increase in platelet counts was observed 4 years after the time of diagnosis. A further longitudinal study monitoring V617F positive-cells will clarify the process of progression from IE to PV in such a patient.

Cytogenetic and molecular aspects of Philadelphia negative chronic myeloproliferative disorders: clinical implications

Chronic myeloproliferative disorders (CMPD) are clonal disorders of the hematopoietic stem cell. The myeloid lineage shows increased proliferation with effective maturation, while peripheral leukocytosis, thrombocytosis or elevated red blood cell mass are found. In Philadelphia negative CMPD recurrent cytogenetic abnormalities occur, but no specific abnormality has been defined to date. The spectrum of cytogenetic aberrations is heterogeneous ranging from numerical gains and losses to structural changes including unbalanced translocations. The most common chromosomal abnormalities are 20q-, 13q-, 12p-, +8, +9, partial duplication of 1q, balanced translocations involving 8p11 and gains in 9p. Cytogenetic analysis of CMPD by conventional or molecular techniques has an important role in establishing the diagnosis of a malignant disease, adding also more information for disease outcome. Molecular studies may detect the possible role of candidate genes implicated in the neoplastic process, addressing new molecular target therapies. FIP1L1/PDGFRalpha rearrangements, as well as alterations of PDGFRbeta or FGFR1 gene have been found to be associated with specific types of CMPD. Recently, a novel somatic mutation, JAK2V617F, has been reported in most of the polycthemia vera (PV) patients, as well as in a lower percentage in essential thrombocythemia (ET) or idiopathic myelofibrosis (IMF) patients. This finding represents the most important advance in understanding of the molecular mechanisms underlined the pathogenesis of CMPD, contributing to the classification and management of patients.

Usefulness of JAK2V617F mutation in distinguishing idiopathic erythrocytosis from polycythemia vera

Idiopathic erythrocytosis (IE) is a primary erythrocytosis not fulfilling the criteria for polycythemia vera (PV) diagnosis. In order to verify the relationship between IE and PV, we screened JAK2V617F mutation in a consecutive series of 11 IE and, for comparison, in 15 PV. JAK2V617F mutation was screened by both cDNA sequencing and mutation specific PCR in both peripheral blood and bone marrow samples. All 11 IE tested negative for JAK2V617F mutation, which, conversely, occurred in 11/15 (73.3%) PV. Our results demonstrate that JAK2V617F is absent in IE and may represent a useful molecular marker for distinguishing IE from PV.

Idiopathic erythrocytosis and other non-clonal polycythemias

Idiopathic erythrocytosis (IE) is characterized by an increase of red blood cell mass without an identified cause. Its diagnosis is based on the exclusion of polycythemia vera (PV), secondary acquired polycythemias and various congenital primary and secondary polycythemias. The frequency of IE has been estimated to be 1.1 per 1000 subjects, which is higher than that observed in PV. Heterogeneous mechanisms underlying IE have been suggested, including 'early' PV and unrecognized secondary or congenital polycythemia. However, the transition of a patient initially classified as IE into PV is a rare occurrence, when more sophisticated diagnostic techniques are employed. IE is a stable disease with a low thrombotic risk and a low, if any, tendency to spontaneous progression to acute leukemia or myelofibrosis. Phlebotomy in patients with IE is controversial. Myelosuppressive drugs should be avoided since their use is associated with evolution into acute leukemia in about 10% of patients.

The diagnosis of polycythemia vera: New tests and old dictums

Pathogenetically fundamental observations have identified polycythemia vera (PV) as a clonal stem cell disease with bone marrow histological and other biological features that distinctly differentiate it from other causes of 'increased' hematocrit. However, relatively little attention has been given to the effective utilization of pathology and laboratory markers of clonal myeloproliferation as diagnostic tools in PV. In contrast, the diagnostic use of red cell mass (RCM) measurement in PV stemmed from the accidental endorsement, as 'diagnostic criteria', of 'study eligibility criteria' that were formulated for clinical trials. It has since become evident that RCM measurement is a tedious procedure that is fraught with multiple-level imprecision, as well as suboptimal diagnostic accuracy. Therefore, it is reasonable to consider dispensing with RCM measurement as a diagnostic test for PV and instead utilize a diagnostic algorithm that combines clinical information with easily accessible laboratory data, including serum erythropoietin level and bone marrow histology. Recent discoveries of myeloproliferative-disease-specific molecular markers, including the JAK2 V617F tyrosine kinase mutation that is found in the majority of patients with PV, provide further support for such a measure.

Familial and congenital polycythemias: a diagnostic approach

The rare absolute polycythemias with an innate and hereditary character can be grouped together under the heading "familial and congenital polycythemias" (FCPs). Primary forms, due to an intrinsic defect in the erythroid progenitor cells, and secondary forms, resulting from extrinsic factors such as an elevated erythropoietin level, have both been reported. Despite the widely divergent characteristics of the different FCPs, the range of possible diagnoses is much more restricted and the distribution of disorders markedly different compared with polycythemias in general. Therefore, in FCP, one can argue against following the algorithm of the Polycythemia Vera Study Group for the evaluation of an elevated hematocrit level, following instead a more specific algorithm. In this article the authors describe a child with primary FCP, review the different FCPs, and propose an adapted work-up scheme.

[Inherited polycythemia]

PURPOSE

The majority of polycythemias occurs sporadically without any other familial case. Very occasionally polycythemia finds a familial support. This work is a review of the actual knowledge about inherited polycythemias.

CURRENT KNOWLEDGE AND KEY POINTS

Although polycythemias linked to a anomaly of the haemoglobin affinity for oxygen are well understood (haemoglobin mutants with high oxygen affinity, 2-3 Diphosphoglycerate deficiency and methemoglobinemia), so called primary polycythemias (above all primary familial and congenital polycythemias) just begin to find an explanation for ten years (erythropoietin receptor gene mutation).

FUTURE PROSPECTS AND PROJECTS

Progressively, the part of really idiopathic polycythemias is smaller and smaller. Although most of mechanisms to explain congenital polycythemias are understood, some of them are still unresolved (Chuvash polycythemia, the majority of primary familial and congenital polycythemias).

Life-threatening thrombotic complications of relative polycythaemia

Relative polycythaemia refers to raised haematocrit with normal red cell mass. Plasma volume may be reduced. This condition is associated with acute hypoxia, smoking, alcohol and diuretics. We describe two life-threatening thrombotic events in two patients with relative polycythaemia under age 40 years. The first had myocardial infarction and on admission haemoglobin was 21.6 g dL-1. The second developed pulmonary embolism and haemoglobin was 19.1 g dL-1. Both patients received antithrombotic measures and isovolumetric venesection. Sixteen patients (age <40 years) who attended our accident and emergency department in 1 year had a haemoglobin level of >18.0 g dL-1. Recognition of relative polycythaemia in at risk-individuals may help reduce thrombotic risk.