A patient with a right cerebellar hemisphere lesion will demonstrate which combination of signs?
- A Ipsilateral (right-sided) limb ataxia, dysmetria, intention tremor, and past-pointing ✓
- B Contralateral (left-sided) limb ataxia due to double decussation
- C Bilateral truncal ataxia and nystagmus only
- D Ipsilateral hemiplegia with cerebellar signs
Correct answer: A. Ipsilateral (right-sided) limb ataxia, dysmetria, intention tremor, and past-pointing
Explanation
Cerebellar hemisphere lesions produce ipsilateral limb ataxia because the cerebellar output pathway decussates twice — first in the superior cerebellar peduncle crossing to the contralateral red nucleus/thalamus, and again via the corticospinal tract decussation in the medullary pyramid — bringing control back to the ipsilateral side. Features of hemispheric lesions include dysmetria, intention tremor, dysdiadochokinesia, past-pointing, and nystagmus with fast phase toward the lesion. Midline (vermis) lesions cause truncal ataxia.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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