Master the board step 3

Master the Boards: USMLE Step 3
Polycythemia Vera (Pvera)
Pvera presents with headache, blurred vision, dizziness, and fatigue.
Pruritus, described as happening after a hot bath or shower, also occurs
from the release of histamine from basophils. Splenomegaly is common.
The key to the diagnosis is a markedly high hematocrit in the absence of hypoxia
with a low MCV. The erythropoietin level will be low. The white cell count and
platelet count can also be elevated. The high hematocrit can lead to thrombosis.
JAK2 mutation is found in
Pvera and ET.
Diagnostic Testing
After the CBC shows a high hematocrit, order an arterial blood gas to exclude
hypoxia as a cause of erythrocytosis. If the case is a CCS, order an erythropoietin
level, which should be low; hematology consultation; and nuclear red cell
mass test. The test for the JAK2 mutation is 97% sensitive. The B12 and LAP
levels are elevated in Pvera.
Treatment
Phlebotomy is the best initial therapy. Hydroxyurea is also used to lower the
cell count. Daily aspirin should also be given. Anagrelide is used in the context
of thrombocythemia.
In Pvera on a CCS, order
a B12 level and LAP in
addition to the CBC. If
the question is a “single
best answer” question,
these tests would not be
the single “best initial” or
“most accurate” tests.
Essential Thrombocythemia (ET)
The key feature of ET is a markedly elevated platelet count. ET presents with
headache, visual disturbance, and pain in the hands referred to as erythromelalgia.
The most common causes of death are bleeding and thrombosis,
with thrombosis being more common.
Therapy is with hydroxyurea to lower the platelet count. Anagrelide is an agent
specific to the treatment of ET but it is not as strong as hydroxyurea. Daily
aspirin should also be given if patient is thrombosing.
Plasma Cell Disorders
Multiple Myeloma (MM)
The most frequent presentation of MM is with bone pain caused by a fracture
occurring under normal use. The most common causes of death from MM
are the following:
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Infection: Patients with multiple myeloma are effectively immunodeficient.
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Renal failure
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