Nonhepatic hyperammonemic encephalopathy following bariatric surgery: A systematic review

Nasser Sakran, Chetan Parmar, Sjaak Pouwels

Research output: Contribution to journalReview articlepeer-review


Background: Nonhepatic Hyperammonemic encephalopathy (NHAE) following Bariatric Surgery (BS), mainly Roux-en-Y Gastric Bypass (RYGB) and Biliopancreatic Diversion (BPD) is a potentially devastating condition if not diagnosed and managed promptly. Methods: A literature review was performed using PRISMA guidelines. Eighteen studies and 3 conference abstracts with a total of 33 patients were included in this review. Results: Majority (28 patients, 84.8 %) had RYGB. Seven patients (21.2 %) had associated metabolic disorders. 60 % of patients presented with neurological symptoms or signs such as confusion, cognitive and/or psychomotor changes, and decreased reflexes. Two patients presented with status epilepticus. In 30 of the 33 patients an elevated serum ammonia levels was reported (90.9 %). The overall mortality was 39.3 %. Conclusion: NHAE is a rare condition following bariatric surgery (in particular bypass procedures), carrying a high mortality rate. The signs and symptoms are predominantly neurological and may be mistaken for Wernicke's encephalopathy or other more common neurological conditions. Serum ammonia levels should be checked in those who present with these symptoms and signs. Prompt treatment might be life saving in patients with NHAE.

Original languageEnglish
Pages (from-to)458-467
Number of pages10
JournalObesity Research and Clinical Practice
Issue number6
StatePublished - 1 Nov 2023
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2023 Asia Oceania Association for the Study of Obesity


  • Bariatric surgery
  • Complications
  • Encephalopathy
  • Gastric bypass surgery
  • Hyperammonemia
  • Nutritional deficiencies
  • Urea cycle


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