Thalamic ataxia.

Seventeen patients with hemiataxia as a manifestation of thalamic infarction were studied. Hemiataxia had the main clinical characteristics of a "cerebellar type" of ataxia, though it never occurred in isolation, being associated with ipsilateral sensory disturbance (hemiataxia-hypaesthesia) in 7 patients, with ipsilateral sensory disturbance and hemiparesis (hypaesthetic ataxic hemiparesis) in 8 patients, and with hemiparesis (ataxic hemiparesis) in 2 patients. Recovery was good, and in all patients the sensory and motor disturbances improved or cleared before the hemiataxia. All patients had an infarct involving the lateral part of the thalamus (thalamogeniculate territory in 16, tuberothalamic territory in 1), also affecting the posterior limb of the internal capsule (PLIC) in 7 patients. Hemiataxia seemed linked to involvement of the caudal part of the ventral lateral nucleus of the thalamus or the immediately adjacent medial part of the PLIC. These structures are near the corticospinal pathways and the ventral posterior nucleus of the thalamus, explaining why hemiataxia is associated with hemiparesis or hypaesthesia in this type of infarct.