Diagnostic methods in hepatic encephalopathy

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome in patients with liver disease and/or portosystemic shunting that affects quality of life and prognosis. The diagnosis is primarily based on clinical criteria that classify HE into 5 grades of severity ranging from normal mental status (grade 0) to coma (grade 4). As this clinical classification is rather subjective, additional diagnostic methods are required. Biochemical diagnostic tests can be used to confirm or exclude the diagnosis and to monitor the effect of treatment. An elevated ammonia level plays a central role in the pathogenesis of HE and can be determined in arterial, venous and capillary blood. Neuropsychological and neurophysiological tests are more sensitive and objective in diagnosing HE than the clinical criteria. Neuropsychological tests are especially of great value because of their high sensitivity for the detection of minimal HE and their low costs. The more sophisticated diagnostic tests such as magnetic resonance spectroscopy or positron emission tomography are mainly used for investigational purposes. This review will highlight these different diagnostic methods and comment on its pitfalls, clinical significance and overall applicability.