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Ataxia is the inability to produce smooth, intentional movements. Ataxia and gait disturbances are not disease entities themselves, but are manifestations of either systemic or nervous system conditions.
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Key symptoms suggesting disease processes beyond the sensory and motor systems include headache, nausea, fever, and decreased level of alertness. The physical examination may also show abnormalities outside the nervous system. Orthostatic vital sign changes point to systemic illness.
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Once the physician has determined that ataxia is the principal problem and not a manifestation of broader illness, the examination should attempt to differentiate between sensory and motor causes of ataxia. While cerebellar lesions may cause ataxia, isolated cerebellar lesions are not the most common cause. Dysmetria (undershoot or overshoot of movements) may be elicited by finger to nose testing. Dysdiadochokinesia (clumsy rapid alternating movements) may be seen when the patient alternately flips their palms and backs of their hands on their thighs. Both of these are suggestive of cerebellar causes. Having the patient slide one heel down the opposite shin is useful for distinguishing between cerebellar and sensory causes. Overshoot of the knee or ankle signifies cerebellar disease, while a wavering course down the shin suggests a deficit of proprioception.
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Vibration and position sense in the toes test the posterior columns, which degenerate in tabes dorsalis (neurosyphilis) and vitamin B12 deficiency. Nystagmus suggests an intracranial cause. In the Romberg test, the patient is asked to stand with arms at sides. Significantly worsening instability with eye closure (a positive Romberg sign) suggests that the patient is relying on visual input for balance caused by a sensory ataxia including posterior column disease or vestibular dysfunction. Instability with the eyes still open suggests a cerebellar lesion.
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Observing the patient rise from a chair and walk on heels and toes may expose subtle proximal or distal weakness. Tandem walking (heel to toe) may elicit subtle ataxia. A motor ataxic gait is characterized by broad-based, unsteady steps. Sensory ataxia with loss of proprioception may be notable for abrupt movements and slapping of the feet with each impact. A senile gait that is slow, broad based, and with a shortened stride may be seen with aging, but also with neurodegenerative disease such as Parkinson disease and normal pressure hydrocephalus. Parkinson disease may also show a festinating gait that is narrow-based, with small shuffling steps that become more rapid. Peroneal muscle weakness causes foot drop, known as an equine gait.
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Table 143-1 shows common causes of acute ataxia and gait disturbances.
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