A Case of Hydroxyurea Intolerant Polycythemia Vera - Episode 3
Ruben Mesa, MD:This individual clearly both demonstrates evidence of resistance and intolerance. The individual has a clear elevation in the counts and needing a phlebotomy, and having a very high and dangerous hematocrit for being this deep into therapy. So, that truly suggests an aspect of resistance.
The individual also has developed a leg ulcer. And leg ulcers are a potential direct toxicity from hydroxyurea. It’s important that physicians recognize this. It’s linked to hydroxyurea in that, one, it’s a direct toxicity and it’s a difficult one for patients. But, two, it typically does not have really even a chance of healing unless the patient is completely off the hydroxyurea. It does not seem to be a dose-related phenomenon. So, just lowering the dose will not be beneficial. This individual, both by current European leukemia criteria and that criteria for hydroxyurea resistance and intolerance, would actually fit both categories of resistance and intolerance. This individual has been started on ruxolitinib, which is both appropriate and consistent with our current guidelines.
With this individual, clearly the symptoms of the difficult splenomegalies tell me that that part is not adequately controlled; that abdominal fullness, that discomfort. They have symptoms to truly suggest perhaps some degree of compromised blood flow in the CNS with difficulties with concentration. I might find if I were able to question the individual that they might have difficulties with short-term memory, concentration, difficulties with reading. They have some difficulties with fever that sometimes can be a sign of toxicity from hydroxyurea. It sometimes can be a sign of progression. So, one might try to tease that out a little bit over time, clearly as the hydroxyurea were to be discontinued.
But finally, the leg ulcer itself. That’s quite painful, it’s prone to infection. Clearly, if it gets severe enough, it even can risk amputation. So, without question, try to reverse that, and that includes cessation of hydroxyurea, but they are slow to heal. It clearly also includes good and adequate wound care.
The risk of thrombosis in polycythemia vera includes many things. Both hematocrit over 45 is clearly a higher risk. And to some degree, the more extreme the value over 45, the greater that risk becomes. So, this individual really demonstrates a very high-risk situation given the height of the hematocrit that they have been able to achieve.
There is only a subset of patients with polycythemia vera who really get over a hematocrit of 60. For one, that is a huge red flag. Second is really the leukocyte count. The leukocyte count, over 11, has been shown through multiple studies and done in multiple complementary ways to increase the rate of thrombotic events. And our European LeukemiaNet response rate criteria relooked for controlling that value to a value of under 11 and, in my estimation, really normalizing that white blood cell count as a key important part of controlling that risk.
Now, the pathophysiology behind it is that as clots form, there really are not accumulations of just red blood cells. Clearly, there is an interaction between the elevated white blood cell count, the elevated platelet count when it’s present, and the elevated hematocrit. All of those things are factors as thrombosis forms, and hence the normalization of those values has a protective effect.
Change in therapy for a patient with polycythemia vera can include many aspects, of which this individual probably manifests several of them. This degree of elevation in the counts while being on active therapy clearly demonstrates resistance to hydroxyurea therapy, from the extreme values of the hematocrit, white blood cell count, etc.
Next is really the increase in the size of the spleen. It shows resistance, the difficulty in symptoms, as well as clearly the toxicity from the hydroxyurea. And it’s not uncommon for both resistance and toxicity to be present. Indeed in part because we’re pushing that dose of hydroxyurea to try to achieve a response, but the patient really isn’t responsive to the hydroxyurea. So, we gain more toxicity but we don’t necessarily gain any more efficacy.
Transcript edited for clarity.