I am going to answer the sample USMLE Step 1 Questions with Explanation. These questions are available at USMLE.org
Q- A previously healthy 19-year-old man is brought to the emergency department 30 minutes after he collapsed while playing softball. He had severe, sharp, upper back pain prior to the game. He is 196 cm (6 ft 5 in) tall. His temperature is 37°C (98.6°F), pulse is 130/min, respirations are 24/min, and blood pressure is 80/50 mm Hg. Physical examination shows pallor and no jugular venous distention. Breath sounds are clear. The carotid pulses are weak. A grade 4/6, late diastolic murmur is heard at the lower left sternal border.
Which of the following is the most likely cause of this patient’s cardiac findings?
(A) Atrial septal defect
(B) Mitral stenosis
(C) Papillary muscle rupture
(D) Perforated tricuspid valve
(E) Stretched aortic anulus
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Answer
This is most likely a case of Marfan Syndrome causing acute aortic dissection. His tall stature, acute severe upper back pain, and cardiovascular instability (hypotension, tachycardia, weak carotid pulses) are classic findings. The diastolic murmur over the lower left sternal border suggests aortic regurgitation, which commonly occurs in aortic dissection when the dissection involves the aortic root and stretches the aortic annulus.
The correct answer is E