Characteristics of minimal hepatic encephalopathy.

The term minimal hepatic encephalopathy refers to the subtle changes in cognitive function, electrophysiological parameters, cerebral neurochemical/neurotransmitter homeostasis, cerebral blood flow, metabolism, and fluid homeostasis that can be observed in patients with cirrhosis who have no clinical evidence of hepatic encephalopathy. Use of this term emphasizes the fact that the entity of hepatic encephalopathy is a single syndrome with quantitatively distinct features relating to severity. The absence of clinical evidence of hepatic encephalopathy is key to the diagnosis and can only be determined by a detailed assessment of the patients' history and a comprehensive neurological assessment of consciousness, cognitive, and motor function. The neuropsychological features of minimal hepatic encephalopathy point to a disorder of executive functioning, particularly selective attention and psychomotor speed, but other abnormalities may be observed. Alterations in electrophysiological variables have been described; endogenous evoked potentials are, in principle, more likely to reflect the presence of minimal hepatic encephalopathy, since they reflect cognitive phenomena rather than mere stimulus conduction but the specificity of the changes observed is unclear at present. Changes have also been described in the execution of diadochokinetic movements and in the capacity to discriminate flickering light, both of which may have diagnostic potential. The changes observed in cerebral blood flow and metabolism in SPET, PET, and 1H and 31P MRS studies reflect the pathogenic process that underlies the condition rather than providing diagnostic information. Similarly, the morphological brain abnormalities identified in this population, including mild brain oedema, hyperintensity of the globus pallidus and other subcortical nuclei observed in cerebral MR studies, and the central and cortical atrophy observed in neural imaging studies, are unlikely to have diagnostic utility. The presence of minimal hepatic encephalopathy is not without clinical consequence; it has a detrimental effect on health-related quality of life, the ability to perform complex tasks such as driving, and on outcome.