Harry Erba, MD, PhD, provides information on the diagnosis and treatment of patients with polycythemia vera: Case 1 - Episode 3
Harry Erba, MD, PhD:Polycythemia vera (PV) should be suspected based on a number of findings that patients may present with. So, first of all, if CBC shows an elevated hemoglobin or hematocrit, then an evaluation or consideration of polycythemia vera should be made. However, there are other symptoms that a patient may present with. Pruritus without a rash would be a sign of polycythemia vera and a number of other myeloproliferative neoplasms. If patients have unexplained fatigue or night sweats, weight loss, unexplained splenomegaly, these are findings that should trigger an evaluation for polycythemia vera.
The criteria for the diagnosis of polycythemia vera have changed over the years. I remember when I was training back around 1990, we used the Polycythemia Vera Study Group criteria for diagnosing polycythemia vera. There were two sets of criteria: the A and the B. The A criteria were: having an elevated red blood cell mass, having splenomegaly, and the absence of hypoxiaso an oxygen saturation above 92%. There were four minor B criterion, and those were: leukocytosis; thrombocytosis; and elevated vitamin B12 binding protein, because granulocytes in the marrow make a lot of transcobalamin II, which elevates B12 levels in the blood; and an elevated leukocyte alkaline phosphatase score.
Some of these tests aren’t even done anymore, so you cannot find a nuclear medicine lab that does a red blood cell mass. Leukocyte alkaline phosphatase is very, very nonspecific, and time consuming, and expensive in the laboratory. And other tests are very nonspecific. And so, there’s been a move to try to revamp the diagnostic criteria for polycythemia vera. And the Europeans have really taken the lead on this. In a subgroup of the European Leukemia Network, new diagnostic criteria have been proposed. These criteria include information about the biology of the disease. So, for example, the JAK2 V617F mutation and the less common exon 12 mutations are now considered part of the diagnostic criteria. In a patient where PV is suspected, these definitely should be checked. This DNA-based assay can be done on peripheral blood. A bone marrow biopsy is not required because the mutation, if acquired, will be found in the nuclei of the white blood cells, as well as erythroid precursors and megakaryocytes in the bone marrow.
The other thing that can be very helpful is the erythropoietin (EPO) level. In a patient with autonomous production of red blood cells, renal production of erythropoietin should be suppressed. So, EPO levels below normal can be very helpful. It’s not a perfect test. It should be done before phlebotomy is started because that can elevate the EPO levels.
Other criteria have been proposed in these diagnostic criteria, such as the EPO-independent in vitro production of blast forming units from peripheral blood; in other words, autonomous red blood cell production from stem cells that are circulating in the blood. But this remains a research test. The Europeans have also suggested that bone marrow biopsies be part of the diagnostic criteria showing a panmyelosis. Unfortunately, some patients, especially with early polycythemia vera may not have a terribly abnormal bone marrow. What has been removed from the diagnostic criteria is the requirement for a red blood cell mass and instead has been replaced with a hemoglobin level that is at the upper end of normal, so that 99% of patients should be below those levels that are defined in the criteria, 18.5 g% for men and 16.5 g% for women.
In making the diagnosis of polycythemia vera, peripheral blood sent for the PCR assay for the JAK2 V617F mutation will detect the disease in 95% to 96% of patients. If you’re highly suspicious of the disease and that assay is negative, then the other test to do is a JAK2 exon 12 mutational analysis. And many laboratories now will do that automatically if the V617F mutation analysis is negative. That’s probably the most important test to do.
If the patient is presenting with splenomegaly, then there’s a long differential diagnosis of splenomegaly that includes both hematologic disorders of hematologic cancers and reactive conditions. If the patient is presenting with erythrocytosis or polycythemia, then the first thing that needs to be ruled out is just a relative polycythemia due to a decrease in plasma volume; in other words, dehydration. If the patient has an absolute erythrocytosis not due to a decrease in plasma volume, then the physician needs to discern whether this red cell elevation is appropriate and physiologically appropriate. For example, any cause of tissue hypoxia will stimulate the kidneys to make EPO. And so, an elevated EPO level should be seen in this situation. These clinical conditions are easy to discover, such as chronic obstructive pulmonary disease, right to left heart shunts, for example. Or they could be more esoteric, like hemoglobinopathies, where hemoglobin has a high affinity for oxygen and doesn’t give oxygen up to tissues, so the tissues are in a relative state of hypoxia.
There could be pathologic causes of erythrocytosis due to erythropoietin production. EPO can be produced by tumors such as renal cell carcinoma, hepatocellular carcinoma, hemangioblastomas. And it’s also been described rarely in benign conditions, such as hydronephrosis or in uterine fibroids. If all of those are ruled out, then polycythemia vera is a likely diagnosis. Finally, there are some congenital causes of erythrocytosis that can be due to abnormalities in oxygen sensing and also the sensitivity of the erythropoietin receptor. These are quite rare, but should be considered in the atypical patient.
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