Clinical study of six patients with pure dysarthria and dysarthria—(Central) facial nerve palsy/isolated central facial nerve palsy caused by extracerebellar infarction

Background: The corticobulbar tract (CBT) exerts bilateral supply to the cerebral nuclei. The cerebellar motor circuit controls the coordination and regulation of voluntary movements including speech function, and consists of input and feedback pathways including the parietopontine fibers (PPFs) which descend along with the CBT. Aim: The pathogenesis of dysarthria caused by ischemic extracerebellar lesions was studied. Methods: Six patients with extracerebellar lesions comprising two patients with pure dysarthria, three patients with dysarthria—(central) facial nerve palsy, and one patient with isolated central facial paresis were enrolled. Results: Lesions were located in the corona radiata in four patients and the posterior limb of the internal capsule (PLIC) in two patients. Lesions were lateralized on the right side in three patients and the left side in three patients. Lesions in the corona radiata and the PLIC included the middle parts where the CBT exists. Conclusions: Based on the hypothesis of bilateral supply to the cerebral nuclei for speech function through the cerebellar motor circuit, it was explicable that unilateral involvement of the PPFs caused dysfunction of the bilateral CBT, which led to the incidence of dysarthria in our case series. Involvement of the PPFs might play a crucial role in the incidence of dysarthria caused by ischemic extracerebellar lesions.