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Neurology and the liver

Neurological syndromes commonly occur in patients with liver disease. A neurological syndrome associated with a liver disease may be a complication of the disease, it may be induced by a factor that also contributes to the disease—for example, alcohol—or it may have no relation to the presence of the liver disease. Neurological deficits associated with liver disease may affect the CNS, the peripheral nervous system, or both. This review focuses on syndromes characterised by altered CNS function associated with structural liver diseases. Space does not permit consideration of peripheral neuropathies associated with liver disease (for example, xanthomatous peripheral neuropathy), diseases of childhood that affect the liver and CNS (for example, Reye’s syndrome), or neurological consequences of hepatic lesions characterised by specific enzyme deficiencies (for example, congenital hyperammonaemias, the porphyrias, kernicterus, galactosaemia, and Zellweger’s syndrome (cerebrohepatorenal syndrome)).

That there is a relationship between the functional status of the liver and that of the brain has been known for centuries.1 The most widely recognised aspect of this relation is that hepatocellular failure may be complicated by the behavioural syndrome of hepatic encephalopathy, in which neurotransmission in the brain is altered.2 3 Recently, it has been suggested that two other behavioural complications of liver disease, scratching due to pruritus in cholestatic patients4 5 and profound fatigue in patients with chronic cholestasis,6 7 may also be associated with altered neurotransmission in the brain.

### DEFINITIONS AND CLASSIFICATION

The term hepatic encephalopathy refers to the syndrome of neuropsychiatric disturbances that may arise as a complication of acute, subacute, or chronic hepatocellular failure. The syndrome is associated with increased portal-systemic shunting of gut derived constituents of portal venous blood, due to their impaired extraction by the failing liver and, in most instances, their passage through intrahepatic and/or extrahepatic portal-systemic venous collateral channels.

The term portal-systemic encephalopathy …