The thalamic ataxia syndrome.

We identified 10 patients with contralateral ataxia and hemisensory loss following unilateral thalamic lesions. Seven patients had ischemic infarcts, and three had hemorrhages. Hemiparesis, when present, was only a transient finding, whereas ataxia, dysmetria, dysdiadochokinesia, rebound, and hemisensory loss persisted. Two patients had cerebellar outflow tremor. Another developed a severe Déjerine-Roussy pain syndrome. Four patients had lesions of the dominant hemisphere, and two had visual field deficits. None had mutism, aphasia, or astasia. On radiographic evaluation, all patients had lesions in the mid to posterior thalamus, a localization consistent with a lesion of the dentatorubrothalamic and ascending sensory pathways into the thalamus. The thalamic ataxia syndrome has a distinct localizing value that is distinguishable from the ataxic hemiparesis syndrome. Strokes occurring in the ventral lateral and posterior nuclei of the thalamus produce the clinical picture of contralateral "cerebellar" dysfunction and sensory loss with only transient weakness.