I am going to answer the sample USMLE Step 1 Questions with Explanation. These questions are available at USMLE.org
Q- A 27-year-old woman comes to the emergency department because of a 1-hour history of severe shortness of breath. She has just returned from a cross-country flight. She has a history of borderline hypertension. Her temperature is 36.9°C (98.5°F), pulse is 113/min, respirations are 28/min, and blood pressure is 138/85 mm Hg. Physical examination shows that the right calf has an increased circumference compared with the left calf, and there is tenderness behind the right knee.
Which of the following is the most likely underlying cause of this patient’s condition?
(A) Antithrombin III deficiency
(B) Factor V Leiden mutation
(C) Glanzmann thrombasthenia
(D) Protein C deficiency
(E) von Willebrand disease
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Answer
This is a case of pulmonary embolism (PE), likely caused by deep vein thrombosis (DVT). It is manifested by sudden severe shortness of breath after a recent long flight, tachycardia and tachypnea and asymmetric calf swelling and tenderness behind the knee.
Factor V Leiden mutation is the most common inherited thrombophilia in individuals of European descent. It leads to resistance of factor V to degradation by activated protein C, resulting in a hypercoagulable state and increased risk of venous thromboembolism (VTE), including DVT and PE.
The correct answer is B