Prolonged N200 is the early neurophysiologic change in the patient with minimal hepatic encephalopathy

Background. In neurophysiological studies, P300, is well known for reflecting early cognitive impairment in minimal hepatic encephalopathy (MHE). Although P300 is investigated extensively, other early event-related potential (ERP) parameters have not been studied in MHE. Methods. The subjects were 21 adult cirrhotic patients without clinical encephalopathy and 29 normal controls. For neuropsychological testing, number connection tests, A and B (NCT-A, NCT-B), the line tracing test, the serial dotting test (SDT), and the digit symbol test (DST) were performed. For ERP testing, auditory oddball paradigms were used. The N100, P200, N200, and P300 parameters were measured. Results. Cirrhosis had longer neuropsychological performance scores on NCT-A, SDT, and DST than the control group. In neurophysiological test, cirrhotic patients showed longer latencies for N100, P200, N200, and P300 than the control group. Although P300 alteration was not seen in patients without MHE compared to the control group (325.4 +/- 43.3 vs. 345.21 +/- 35.1, p = 0.25), N200 latency was significantly prolonged in cirrhotic patients without MHE compared to the healthy group (242.1 +/- 30.3 vs. 259.58 +/- 33.3, p = 0.006). N200 also showed good correlation with psychometric hepatic encephalopathy score and critical flicker frequency. Conclusions. N200 is a useful tool for assessing early changes of cognitive dysfunction in cirrhosis. It suggests that slower auditory cortical processing is the first sign of cerebral deterioration in patients with hepatic encephalopathy