Hyperammonaemic encephalopathy due to non-functioning urea cycle as a complication to gastric bypass surgery

Hyperammonaemic encephalopathy in the absence of liver failure is a major diagnostic challenge. A rare cause is as a complication to previous gastric bypass surgery, a condition reported to be associated with high mortality. In this case report, we present the exhaustive diagnostic work-up and clinical reversal of deep and recurrent hyperammonaemic encephalopathy in a patient with previous gastric bypass surgery. As a key finding, the patient exhibited an extreme reduction of the in vivo capacity for urea synthesis, which was reverted by long-standing correction of severe protein and micronutrient malnourishment (Functional Hepatic Nitrogen Clearance; 2.9 to 25.5 L/h). In addition, we observed reduced levels of fasting plasma amino acids (α-amino nitrogen; 2.7 to 3.6 mmol/L) and glucagon (0.3 to 2.6 pmol/L) before clinical improvement, which may contribute to the non-functioning urea synthesis. These observations elucidate the underlying pathophysiology of hyperammonaemia as a complication of gastric bypass and highlight a potential mechanism - non-functioning urea cycle as a result of protein malnourishment and hepatic glucagon resistance.