Question: Behavioral Health & Nervous Systems
A 65-year-old man develops progressive gait unsteadiness over several months. On examination he has an intention tremor and dysmetria on finger-to-nose testing on the right side, and he tends to fall toward the right. There is no weakness or sensory loss. Damage to which of the following structures is the most likely cause?
Choose one answer.
Explanation
Correct answer: B. Right cerebellar hemisphere
Lateral cerebellar hemisphere lesions cause ipsilateral limb dysmetria, intention tremor, and a tendency to fall toward the side of the lesion, because cerebellar output crosses twice and ultimately influences the same side of the body. Right-sided signs therefore localize to the right cerebellar hemisphere. The vermis controls truncal and gait stability rather than limb coordination, and internal capsule or frontal lesions would produce weakness or other deficits.
Learning objective: Localize cerebellar hemisphere lesions to ipsilateral limb signs.
Want this back right before you'd forget it?
Ebb Deck brings back 1,500 USMLE Step 1 questions like this one with spaced repetition, on the web and on iPhone. Your first 100 are free.