[Early somesthetic evoked potentials and sensory deficits in thalamic and juxta-thalamic lesions. Clinical, electrophysiological and x-ray computed tomographic study in 70 patients].

Somatosensory Evoked Potentials (SEPs) have been recorded in 70 patients presenting a thalamic or capsular CT scan lesion. The loss of SEP parietal components confirmed the deafferentation of somatosensory cortex in infarctions of geniculothalamic or anterior choroidian arteries territory. SEPs were found to be normal in infarctions of other arterial territories, in agreement with the clinical evidence of normal somatosensory performances. In patients with haematomas, especially when located in the thalamus, there was no clear correlation between lesion sites and SEP data. Abnormal parietal responses were always associated to impaired tactile and joint sensations. The correlation was less significant for vibration sense. In four cases of selective loss of pain sensation SEPs were normal. In seven patients with abnormal parietal responses sterognosis was normal, a situation which is never encountered in cortical lesions. SEPs reliably documented the degree of somatosensory loss in patients with tactile extinction phenomenon. Contralateral parietal responses were reduced in four patients with tactile extinction but no attentional deficit for other sensory modalities. Thus normal SEPs are a prerequisite to consider thalamic neglect syndrome as a pure attentional disorder. Moreover SEPs demonstrated that there was no long-lasting deafferentation of somatosensory cortex in ataxic hemiparesis. It was found that selective loss of post-or prerolandic SEP components could occur in capsular lesions. This finding favors the hypothesis of parallel and independant thalamo-parietal and thalamo-frontal somatosensory projections that may be selectively damaged in lesions of thalamocortical radiations.