Exclude polycythemia vera in patients with erythrocytosis

Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 65-year-old man is evaluated for a 2-year history of daytime somnolence, snoring, and apneic episodes during the night as witnessed by his wife. He does not have blurred vision, tinnitus, or headache. He has no cardiopulmonary symptoms and does not smoke cigarettes. The patient has hypertension for which he takes lisinopril and atenolol.

On physical examination, temperature is normal, blood pressure is 170/98 mm Hg, pulse rate is 72/min, and respiration rate is 18/min. BMI is 44. Oxygen saturation is 95% with the patient breathing ambient air and does not decrease with modest exertion. The patient’s face is erythematous, and his neck is thick. Hepatosplenomegaly is absent.

Laboratory studies:

Hemoglobin	17.5 g/dL (175 g/L)
Leukocyte count	5000/µL (5.0 × 10⁹/L)
Platelet count	225,000/µL (225 × 10⁹/L)
Erythropoietin	35 mU/mL (35 units/L)

Which of the following is the most appropriate management?

A) Initiate hydroxyurea
B) Order sleep study
C) Perform bone marrow biopsy
D) Perform phlebotomy

MKSAP Answer and Critique

The correct answer is B) Order sleep study. This item is available to MKSAP 16 subscribers as item 25 in the Hematology and Oncology section.

This patient requires a sleep study to diagnose obstructive sleep apnea and nocturnal oxygen desaturation as a cause of secondary erythrocytosis. The diagnosis of secondary erythrocytosis is suggested by the elevated hemoglobin concentration and elevated erythropoietin level. In patients with polycythemia vera (PV), the erythropoietin level is suppressed. The most common cause of secondary erythrocytosis is hypoxic pulmonary disease. However, this patient’s oxygen saturation is normal at rest and following modest exertion. Nocturnal oxygen desaturation due to obstructive sleep apnea is also a cause of secondary erythrocytosis, and this diagnosis is suggested by his snoring, obesity, and increased neck size, as well as his witnessed apneic episodes. If obstructive sleep apnea is confirmed by polysomnography, the patient’s management would include continuous positive airway pressure.

PV is characterized by nonspecific symptoms including tinnitus, blurred vision, headache, and more specific symptoms including generalized pruritus that often worsens after bathing, erythromelalgia (a burning sensation in the palms and soles possibly caused by platelet activation), and splenomegaly, none of which are present in this patient. In addition, his leukocyte and platelet counts are not elevated as they often are in PV, and his elevated erythropoietin level essentially excludes PV. Treatment of PV is directed toward reducing the red blood cell mass and preventing thrombosis. Therapeutic phlebotomy and low-dose aspirin is the primary therapy for most patients. Hydroxyurea is often used in older symptomatic patients whose disorder cannot be controlled with phlebotomy and aspirin alone. Because this patient does not have PV, phlebotomy, low-dose aspirin, and hydroxyurea are not indicated.

An increased number of megakaryocytes and a hypercellular bone marrow are characteristic of PV, but bone marrow findings are not part of the Polycythemia Vera Study Group diagnostic criteria. Furthermore, although a hypercellular bone marrow is likely in a patient with secondary erythrocytosis, this finding does not establish the cause of the condition.

Key Point

In patients with confirmed erythrocytosis, an elevated serum erythropoietin level helps exclude polycythemia vera and suggests the presence of secondary erythrocytosis.

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