What is the significance of a severely elevated white blood cell (WBC) count in a patient with resolving pneumonia and polycythemia vera (PV)?

From the Guidelines

A white blood cell count of 62,000/μL is severely elevated and requires immediate attention in a patient with resolving pneumonia and polycythemia vera, with a focus on reducing the white cell count using hydroxyurea as the first-line cytoreductive therapy, starting at 500-1000 mg daily, as recommended by the NCCN guidelines 1. The management should also focus on treating the underlying causes, including the pneumonia, with appropriate antibiotics based on culture results or empiric coverage if cultures are unavailable. The elevated white count likely represents a combination of the myeloproliferative disorder (polycythemia vera) and an inflammatory response to the pneumonia. Polycythemia vera commonly causes elevated white blood cells alongside increased red cells and platelets due to abnormal bone marrow proliferation from JAK2 mutations, which increases the risk of thrombotic events, as noted in a study published in the American Journal of Hematology 1. As the pneumonia resolves, the white count may decrease somewhat, but cytoreductive therapy will likely be necessary to manage the underlying polycythemia vera. Regular monitoring of complete blood counts is essential to track response to treatment and adjust medication dosing accordingly. For acute management, consider leukapheresis if there are symptoms of leukostasis. It is also important to manage cardiovascular risk factors and consider aspirin for vascular symptoms, as recommended by the NCCN guidelines 1. A study published in the Journal of the National Comprehensive Cancer Network found that hydroxyurea was effective in reducing the risk of thrombotic complications in patients with polycythemia vera 1. Therefore, the use of hydroxyurea as the first-line cytoreductive therapy is supported by the evidence, and its benefits in reducing the risk of thrombotic events and managing the underlying polycythemia vera make it the recommended treatment option.

Some key points to consider in the management of this patient include:

• The use of hydroxyurea as the first-line cytoreductive therapy, starting at 500-1000 mg daily, with dose adjustments based on blood count response
• The importance of managing cardiovascular risk factors and considering aspirin for vascular symptoms
• The need for regular monitoring of complete blood counts to track response to treatment and adjust medication dosing accordingly
• The consideration of leukapheresis for acute management if there are symptoms of leukostasis
• The treatment of the underlying pneumonia with appropriate antibiotics based on culture results or empiric coverage if cultures are unavailable.

From the Research

Severe White Cell Count in Polycythemia Vera

• A severe white cell count of 62 in a patient with resolving pneumonia and polycythemia vera is a significant concern, as polycythemia vera (PV) is a myeloproliferative neoplasm characterized by an increased risk of thrombosis 2.
• Leukocytosis, or an elevated white blood cell count, is a common feature of PV, occurring in approximately 49% of patients 2.
• The presence of a JAK2 gene variant is a key diagnostic criterion for PV, and is found in more than 95% of patients 2.

Management of Polycythemia Vera

• The management of PV typically involves therapeutic phlebotomy to maintain a hematocrit of less than 45%, as well as low-dose aspirin to reduce the risk of thrombosis 2, 3.
• Cytoreductive therapy, such as hydroxyurea or interferon, may be recommended for patients at high risk of thrombosis, including those with a history of thrombosis or age 60 years or older 2, 3.
• In cases where patients are resistant or intolerant to hydroxyurea, alternative therapies such as interferon, ruxolitinib, or other agents may be considered 4.

Treatment Options for High-Risk Patients

• For high-risk patients with PV, cytoreductive therapy is often necessary to reduce the risk of thrombosis, and may involve the use of hydroxyurea, interferon, or other agents 5, 6.
• Novel therapeutic approaches, such as pegylated interferon and MDM2 inhibitors, are being developed and may offer promising alternatives for the treatment of high-risk PV patients 6.