P4859 - Hyperammonemia Following Roux-en-Y Gastric Bypass: A Life-Threatening Complication

Lital Aliasi-sinai, MD¹, Destiny Nguyen, MD², Bruce Gelman, MD²
1Mount Sinai West, Icahn School of Medicine at Mount Sinai, New York, NY; 2Mount Sinai Morningside, Icahn School of Medicine at Mount Sinai, New York, NY

Introduction: Hyperammonemia is a rare but potentially fatal complication following Roux-en-Y gastric bypass (RYGB), often presenting with altered mental status (AMS) and rapid neurological decline. Early recognition is critical, as delayed diagnosis can result in cerebral edema, coma, and death. Although mechanisms remain unclear, proposed contributors include altered gut microbiota, nutritional deficiencies, and unmasked or acquired urea cycle disorders.

Case Description/

Methods: A 55-year-old woman with a history of obesity, chronic back pain, depression and prior RYGB 19 years ago with revision and distalization 3 years ago presented with subacute weakness, anorexia and depressed mental status. On presentation, she had anasarca, hypoalbuminemia (1.3 g/dL) and hepatic steatosis without cirrhosis. Initial work up for AMS was unrevealing, without evidence of infection, stroke or significant metabolic derangement. She developed worsening encephalopathy with myoclonus and asterixis. Additional labs revealed zinc deficiency (26 µg/dL), elevated ammonia (initially 84.9 µmol/L, peaking at 220 µmol/L), normal glutamine (379 µmol/L) and citrulline (19.6 µmol/L). Despite rectal lactulose, encephalopathy progressed, with development of acute hypoxic respiratory failure leading to ICU admission. MRI was consistent with hepatic encephalopathy; vEEG revealed diffuse cortical hyperexcitability. She was treated with lactulose, rifaximin, L-carnitine, continuous venovenous hemofiltration, and aggressive nutritional repletion including zinc. Her course was complicated by ARDS, ventilator-associated pneumonia and suspected cerebral edema requiring hypertonic saline. She eventually improved, was weaned to tracheostomy collar, and discharged to subacute rehabilitation.

Discussion: Post-RYGB related hyperammonemia is under-recognized, with less than 30 cases reported. Onset ranges from 1 month to 28 years post-operation, with a reported 50% mortality. Common features include AMS, signs of severe malnutrition, elevated ammonia and often glutamine, hypoalbuminemia, and zinc deficiency. Management includes ammonia-lowering therapies, acute protein restriction with adequate caloric support, and nutritional repletion, especially zinc, to restore urea cycle function. This case highlights the need to consider hyperammonemia in the differential for AMS in post-RYGB patients and underscores the importance of early recognition and intervention in this potentially reversible condition.

Disclosures:
Lital Aliasi-sinai indicated no relevant financial relationships.
Destiny Nguyen indicated no relevant financial relationships.
Bruce Gelman indicated no relevant financial relationships.

Lital Aliasi-sinai, MD¹, Destiny Nguyen, MD², Bruce Gelman, MD². P4859 - Hyperammonemia Following Roux-en-Y Gastric Bypass: A Life-Threatening Complication, ACG 2025 Annual Scientific Meeting Abstracts. Phoenix, AZ: American College of Gastroenterology.