Minimal hepatic encephalopathy: diagnosis by neuropsychological and neurophysiologic methods

Minimal hepatic encephalopathy (mHE) consists of cognitive deficits found on neuropsychological and/or neurophysiologic methods in patients with liver disease, present most commonly in cirrhosis. Patients suffering from mHE may have psychomotor slowing and cognitive deficits affecting their ability to perform many activities of daily life, especially driving and other activities requiring subtle cognitive abilities. It has been now been shown that patients with mHE improve after treatment with agents like lactulose and other therapeutic interventions. Neuropsychological and neurophysiologic tests have been widely used and have shown the greatest promise for the detection of mHE. Commonly used psychometric tests include trailmaking tests (number and figure connection tests) and Wechsler Adult Intelligence Scale (WAIS) for verbal and performance skills. Among the various neuropsychological or psychometric tests, trailmaking tests and block design and digit symbol tests from WAIS-performance battery appear to be adequate for diagnosis of mHE. Standardized tests including NCT A and B, line tracing, serial dotting test and digits-symbol test (PSE syndrome test) validated in German patients need validation in other populations. Both exogenous evoked potentials and endogenous event-related potentials have been used extensively in diagnosing mHE. However, the event-related P300 wave is the most consistent wave and can be considered the electrophysiological counterpart of the psychometric tests as both involve active use of the cognitive faculties. Other new tests like the critical flicker frequency have shown some promise but further studies are required to substantiate initial results. In conclusion, a combination of at least two psychometric (trailmaking tests [NCT or FCT], block design and digit symbol test) and neurophysiological tests (P300 auditory evoked potential or electroencephalography with mean dominant frequency) appears to be optimal in detecting mHE.