Furthermore, diseases other than those of the cerebellum can cause ataxia that closely simulates the cerebellar type. The ataxia of severe sensory neuropathy and of posterior column or posterior spinal root disease (sensory ataxia) simulates cerebellar ataxia; presumably this is a result of involvement of the large peripheral spinocerebellar afferent fibers. Tabes dorsalis and sensory ganglionopathy are prime examples of this type of disorder. However, there should seldom be difficulty in separating cerebellar from sensory ataxia if one takes note of the loss of distal joint position sense, absence of associated cerebellar signs such as dysarthria or nystagmus, loss of tendon reflexes, and the corrective effects of vision on sensory ataxia. In peripheral neuropathy and in spinal cord disease with ataxia, the Romberg sign is invariably present, reflecting a parallel dysfunction of large afferent fibers in the posterior columns; this sign is not found in lesions of the cerebellar hemispheres except that the patient may initially sway with eyes open, and a bit more with eyes closed.
A cerebellar type of tremor reaches an extreme form in the large-fiber polyneuropathy related to antibodies against myelin-associated glycoprotein but the features are closer to an enhanced action tremor, as discussed in Chap. 43. In the Miller Fisher syndrome, which is considered to be a version of acute Guillain-Barré polyneuropathy, sensation is intact or affected only slightly and the severe ataxia and intention tremor are presumably a result of a selective peripheral disorder of spinocerebellar nerve fibers. Disorders of these same fibers in the spinocerebellar tracts of the cord may produce similar sensory-ataxic effects; subacute compressive lesions such as thoracic meningioma or demyelinating lesions are the usual causes. Again, there is a prominent Romberg sign. Occasionally, a cerebellar-like tremor in one limb results from a lesion in the dorsolateral cord or roots that selectively interrupts afferent fibers, presumably those directed to the spinocerebellar tracts.
Intense vertigo produces a special ataxia of gait and that is distinguished by reeling from side-to-side and listing to one side, past pointing, and torsional-rotatory nystagmus, as discussed in Chap. 14. The nonvertiginous ataxia of gait caused by vestibular paresis (e.g., streptomycin toxicity) has special qualities, which are described in Chap. 6. Vertigo and cerebellar ataxia may be concurrent, as in some patients with a paraneoplastic disease and in those with infarction of the lateral medulla and inferior cerebellum. An unusual and transient ataxia of the contralateral limbs occurs acutely after infarction or hemorrhage in the anterior thalamus (thalamic ataxia); in addition to characteristic signs of thalamic damage, there may be an accompanying unilateral asterixis. Finally, a lesion of the superior parietal lobule (areas 5 and 7 of Brodmann) rarely results in mild ataxia of the contralateral limbs.
Differential Diagnosis of Cerebellar Disease