Features and assessment of hepatic encephalopathy

Hepatic encephalopathy is characterised by a range of neuropsychiatric symptoms and signs (including coma) that can develop in severe liver disease. Encephalopathy occurs in both acute liver failure and in chronic liver disease (usually cirrhosis).

Features of encephalopathy include changes in cognition, personality and emotions, sleep disturbances, and disorientation. A diagnosis of encephalopathy may be supported by impaired ability to draw or construct objects (eg a 5-pointed star), elevated arterial ammonia concentration, and changes on electroencephalogram (EEG). Routine measurement of serum ammonia concentration is rarely helpful. A flapping tremor (asterixis) strongly supports a diagnosis of encephalopathy; however, it is not specific to severe liver disease.

Hepatic encephalopathy can be classified as covert or overt. Covert hepatic encephalopathy describes a state of low-level, often subtle, cognitive dysfunction that cannot be readily detected on routine clinical examination (eg impaired concentration and decision-making ability, sleep disturbance, subtle personality changes). Diagnosis can be made using specialised psychometric or psychophysiological tests. Overt hepatic encephalopathy is characterised by reproducible physical signs consistent with more global and obvious neurological impairment (eg flapping tremor, disorientation, drowsiness, coma).

Formal assessment for covert hepatic encephalopathy is recommended to identify patients at increased risk of motor vehicle accidents, falls, poor work performance and progression to overt hepatic encephalopathy. EncephalApp is a sensitive tool for detecting cognitive impairment and has been validated for this indication.

Fitness to drive can be affected by unpredictable manifestations of encephalopathy including drowsiness, disorientation, confusion and prolonged reaction time. Patients with episodic overt hepatic encephalopathy should not drive, even if they are receiving medical treatment. Assessing fitness to drive in patients with covert encephalopathy is complex and may require a combination of specialist assessment, neuropsychiatric testing and formal driving assessment (for details, see the Austroads website).