Hyperammonemia can lead to serious outcomes including brain herniation, coma and death. It is often attributed to liver disease, specifically in association with alcohol use. However, in the absence of liver pathology, it can be difficult to diagnose the etiology. We present a case of a patient with a history of remote alcohol use disorder in remission and Roux-en-Y gastric bypass (RYGB) 20 years prior who was admitted for altered mental status, found to have hyperammonemia with normal liver function tests and a normal liver biopsy. An extensive workup was unremarkable until several weeks into her admission, where she was found to have osmotic demyelination syndrome on head MRI, which was obtained after she developed persistent myoclonus and opsoclonus. Her osmotic demyelination was speculated to be secondary to hyperammonemia, which itself was correlated to her history of RYGB. There have been multiple case reports on the association of late onset hyperammonemic encephalopathy after RYGB; however, no significant correlation has yet to be made between osmotic demyelination syndrome and hyperammonemia.