Impaired cortico-bulbar tract function in dysarthria due to hemispheric stroke. Functional testing using transcranial magnetic stimulation.

We investigated cortico-lingual and cortico-orofacial tract function utilizing transcranial magnetic stimulation in 18 consecutive patients with dysarthria due to hemispheric stroke. Delayed responses (conduction time > mean + 2.5 SD of that of 43 controls) or absent responses were considered abnormal. In all patients, motor-cortex stimulation of the lesion side demonstrated absent (13 patients) or delayed (five patients) responses to the tongue bilaterally (17 patients) or unilaterally (one patient). In 14 patients the contralateral orofacial responses were either absent (13 patients) or delayed (one patient). According to the electrophysiological findings, all lesions revealed by CT or MRI, were located within the pyramidal tract at the lower motor cortex (n = 4), the corona radiata (n = 7), and the genu of the internal capsule (n = 3) or its posterior limb (n = 4). We conclude that interruption of the cortico-bulbar tract fibres to muscles involved in articulation is a frequent cause of dysarthria in hemispheric stroke.