A positive finger-to-nose test is most consistent with a lesion in which neurological structure?

• A. Cerebellum
• B. Cerebrum
• C. Brainstem
• D. Spinal cord

Answer: (A)

The finger-to-nose test mainly evaluates how well the cerebellum coordinates voluntary movements. To perform it well you must judge distance, direction, and timing, and the cerebellum fine-tunes the movement in real time. When the cerebellum is damaged, you get dysmetria—the limb overshoots or undershoots the target—and often an intention tremor as you approach the nose. This ipsilateral dyscoordination is the telltale sign, making a cerebellar lesion the best explanation for a positive result.

Other regions can cause motor issues, but they don’t produce this characteristic coordination error as cleanly. Cerebral (cortical) lesions typically lead to weakness or planning problems rather than a pure coordination deficit; brainstem or spinal cord issues may cause gait ataxia or sensory loss but the sharp, limb-specific dysmetria on a targeted motion points most directly to cerebellar dysfunction.