Isolated dysarthria due to extracerebellar lacunar stroke: a central monoparesis of the tongue

Objectives-The pathophysiology of dysarthria can preferentially be studied in patients with the rare lacunar stroke syndrome of "isolated dysarthria" Methods-A single study was carried out on seven consecutive patients with s udden onset of isolated dysarthria due to single ischaemic lesion. The loca lisation of the lesion was identified using MRI. The corticolingual, cortic o-orofacial, and corticospinal tract functions were investigated using tran scranial magnetic stimulation. Corticopontocerebellar tract function was as sessed using Te-99m hexamethylpropylene amine oxime-single photon emission computerised tomography (HMPAO-SPECT) in six patients. Sensory functions we re evaluated clinically and by somatosensory evoked potentials. Results-Brain MRI showed the lesions to be located in the corona radiata (n =4) and the internal capsule (n=2). No morphological lesion was identified in one patient. Corticolingual tract function was impaired in all patients. In four patients with additional cortico-orofacial tract dysfunction, dysa rthria did not differ from that in patients with isolated corticolingual tr act dysfunction. Corticospinal tract functions were normal in all patients. HMPAO-SPECT showed no cerebellar diaschisis, suggesting unimpaired cortico pontocerebellar tract function. Sensory functions were not affected. Conclusion-Interruption of the corticolingual pathways to the tongue is cru cial in the pathogenesis of isolated dysarthria after extracerebellar lacun ar stroke.