Cortico-spinal pathways and inhibitory mechanisms in hepatic encephalopathy

Transcranial magnetic stimulation of the cerebral cortex was used to study motor system function in 31 cirrhotics (29 post-necrotic and 2 cryptogenic) with and without hepatic encephalopathy (HE). The results were compared with those of 14 healthy subjects matched for age. A significant increase of central motor conduction time, a significant raising of the motor evoked potential (MEP) threshold at rest and a significant reduction of the MEP/muscle action potential (MAP) amplitude ratio were found only in patients with chronic stable (12 patients) and recurrent (9 patients) HE. Vice versa, a significant shortening of the central silent period was observed in all 31 cirrhotic patients. The peripheral silent period was normal in all instances. These results indicate that the damage to the cortico-spinal pathways is related to the progression of cirrhosis to HE, and that cirrhotic patients present a dysfunction of the inhibitory motor mechanisms before HE is clinically manifest.