Normal gait, stance, and coordination require integrity of the motor, vestibular, cerebellar, and proprioceptive pathways (see also Movement and Cerebellar Disorders). Lesions in these pathways cause characteristic deficits:
Patients with cerebellar ataxia have difficulty maintaining balance and require a wide gait for stability (see table Signs of Cerebellar Disorders).
Footdrop due to motor weakness causes a steppage gait (lifting the leg higher than normal to avoid catching the foot on surface irregularities).
Pelvic muscle weakness causes waddling.
Spastic leg causes scissoring and circumduction.
Patients with impaired proprioception must constantly observe placement of their feet to avoid tripping or falling.
Coordination testing can help detect ataxic movements. Testing maneuvers include
Pointing a finger at one's own nose then to the examiner's finger (finger-to-nose testing)
Running the heel from the opposite knee down the shin (heel-to-shin testing)
Rapidly tapping the index finger to the thumb
Alternating pronation and supination of the hand with increasing speed
Because normal performance of these actions requires intact visual, motor, cerebellar, and proprioceptive pathways, localizing specific anatomic etiologic lesions may be difficult. For example, abnormal results for finger-to-nose or heel-to-shin testing may be caused by motor weakness due to a lesion in the corticospinal pathway or in the cerebellum and its connections. During either maneuver, an intention tremor that causes oscillation from one side to the other suggests cerebellar dysfunction.
