Oral tryptophan challenge studies in cirrhotic patients: no evidence of neuropsychiatric changes

Hepatic encephalopathy is a frequent complication of cirrhosis. Abnormalities of 5-hydroxytryptamine (5-HT) and its metabolites are recognized and may contribute to its pathogenesis. We therefore studied the effect of an oral tryptophan load (6-18 g) upon psychometric test scores and analyzed EEG's in alcoholic cirrhotic patients. Eight patients had had previous encephalopathic episodes related to variceal bleeds and one patient was awaiting a liver transplant. Five out of the 10 patients had at least one abnormal baseline psychometric test. Following tryptophan challenge there were no changes in blood ammonia but plasma tryptophan levels were elevated approximately 10-fold (p < 0.01 x 10(-7)). Nevertheless, there were no statistically significant changes in psychometric testing or analyzed EEG frequency distribution. All patients reported nausea or vomiting while one patient developed a short-lived serotonin like syndrome. We conclude that in this group of patients, an oral tryptophan load does not induce or worsen subclinical hepatic encephalopathy. If the high blood levels of tryptophan seen in these studies are able to influence cerebral neurotransmitter synthesis, the results do not support a primary role for abnormalities of 5-HT neurotransmission in hepatic encephalopathy.