USMLE Step 1 Question

TOPIC: Neurology

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The following is a high-yield USMLE Step 1 exam question.

To get the most out of this practice question deep-dive, I recommend doing the following:

1. Go through the question using our test-taking strategy to ensure you’re tackling the question in the most effective and efficient way (read about it HERE)

2. Formulate your answer and find it in the answer choices

3. If you believe you’ve identified the correct answer, you can scroll to the bottom of the post to see if you’re right; if you are - congrats! Be sure to read through the deep-dive section to extract more knowledge from the question

4. If you aren’t 100% sure about the answer, start with the deep-dive section to get clear on the concept(s), then try to formulate an answer from there; once you believe you’ve found the answer, scroll to the bottom of the page (if you were wrong, re-read the deep-dive to figure out why)

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A 56-year-old male presents to your clinic with a 6-month history of fatigue, weakness, and unsteady gait. He also reports occasional numbness and tingling in his hands and feet. Vital signs are within normal limits. Physical examination reveals a pale patient with decreased vibratory sensation and proprioception in the lower extremities. Laboratory studies show macrocytic anemia with a mean corpuscular volume of 110 fL, elevated methylmalonic acid, and low serum vitamin B12 levels. If left untreated, which of the following consequences is most likely to occur in this patient?

A. Parkinsonism

B. Wernicke-Korsakoff syndrome

C. Progressive multifocal leukoencephalopathy

D. Irreversible neurological damage

E. Dilated cardiomyopathy

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If you want to go right to the answer, it can be found at the bottom of this post. If you want to dissect each answer choice first, read through the ‘DEEP-DIVE” below.

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DEEP-DIVE:

This question describes a patient with symptoms and laboratory findings consistent with a Vitamin B12 deficiency. Vitamin B12 is crucial for