Impaired corticolingual pathways in patients with or without dysarthria after acute monohemispheric stroke

Abstract

The occurrence of dysarthria is not infrequent in stroke but little is known about its pathophysiology. The aims of the present study were to assess the central motor innervation of the tongue in normal adults using transcranial magnetic stimulation (TMS) and to compare this with that seen in stroke patients with or without dysarthria. The study included 46 patients with acute monohemispheric stroke due to occlusion of the territory of the middle cerebral artery as documented by CT brain scan (26 patients with dysarthria and 20 patients without dysarthria). Forty-five (age and sex matched) normal volunteers served as controls. Corticolingual pathways were assessed for each subject after TMS of each hemisphere. TMS over the motor cortex of healthy subjects elicited consistent ipsilateral and contralateral lingual responses. The ipsilateral response was usually smaller and approximately 73% of the amplitude of the contralateral response. The cross talk between the two halves of the tongue as estimated after unilateral electrical stimulation of hypoglossal nerve gave a contra/ipsi ratio of 36%, which was significantly smaller than the ratio seen after cortical stimulation (CL). For the patients, with or without dysarthria, motor evoked potential (MEP) latencies (ipsilateral and contralateral) were significantly prolonged after stimulation of affected hemisphere compared with the non-affected hemisphere or the control group (P< 0.001). MEP amplitudes were significantly smaller in hemiplegic patients with dysarthria compared to patients without dysarthria. In patients without dysarthria stimulation of the unaffected hemisphere tended to evoke responses that were of similar size on both sides. There were no significant associations between neurophysiological parameters and side of infarction. We conclude that interruption of the corticolingual pathways is frequent in stroke patients with or without dysarthria. The ability of unaffected hemisphere to evoke responses in the side contralateral to the lesion may relate to the absence or presence of dysarthria.