Cerebellar Examination

The cerebellum calibrates the rate, rhythm, force, and accuracy of voluntary movement. It also helps integrate vestibular, visual, and proprioceptive information so that posture, gait, balance, eye movements, and speech remain coordinated. Damage therefore produces ataxia—inaccurate or poorly timed movement of the limbs, trunk, gait, or speech—rather than primary weakness or loss of sensation. A patient can generate normal force yet place the heel inaccurately or overshoot a target. A lesion in one cerebellar hemisphere usually causes limb findings on the same side. Cerebellar output pathways double-cross before reaching their functional targets, so a right cerebellar lesion may cause right-arm dysmetria and intention tremor. This differs from many cerebral cortical motor lesions, which produce contralateral weakness. The distribution of incoordination helps with localization. Limb dysmetria and intention tremor suggest hemispheric involvement. Truncal instability, titubation, and marked gait ataxia suggest midline vermis involvement. Nystagmus and impaired balance may reflect involvement of cerebellar systems that coordinate vestibular and ocular function. These patterns are useful clues, not permission to stop looking for a vascular, toxic, inflammatory, or structural cause.