Hyperammonaemic encephalopathy following bariatric surgery: detailed biochemical phenotyping and pathophysiology informed treatment.

Hyperammonaemic encephalopathy is a rare and potentially devastating complication following bariatric surgery. Recognition of the pathology and understanding of pathophysiology are essential to effective treatment. Three patients with symptoms and biochemical changes suggestive of small intestinal bacterial overgrowth (SIBO) following gastric bypass developed relapsing hyperammonaemic encephalopathy. Severe protein malnutrition and biochemical dysfunction of the urea cycle were noted on biochemical testing. Hyperammonemia in all three patients did not respond to empiric therapy for a potential genetic urea cycle disorder. Successful treatment was dependent upon adequate therapy for SIBO in the bypassed small bowel loop and a period of parenterally delivered nutrition. Uncontrolled weight loss was able to be arrested. Hyperammonaemic encephalopathy after bariatric surgery is driven by SIBO and subsequent protein-energy malnutrition. These two preconditions cause increased delivery of ammonia to the urea cycle and cellular dysfunction of the urea cycle. Treatment of these preconditions informs management priorities.