A Mysterious Case of Recurrent Acute Hyperammonemic Encephalopathy

Abstract

Ammonia is a well-recognized neurotoxin. Awareness about hyperammonemia, in the absence of liver cirrhosis, may help in lifesaving, prompt diagnosis, and treatment. We present a case of a 53-year-old male who presented to the emergency department (ED) with altered mental status (AMS). He was unresponsive with occasional eye opening. Initial labs were normal except for mildly elevated blood alcohol level. Serum ammonia levels were very high (305 umol/L). He improved with lactulose. He had similar admissions later on. Urine orotic acid levels were high confirming ornithine transcarbamylase (OTC) deficiency. Noncirrhotic hyperammonemia as a cause of AMS remains a diagnosis of exclusion requiring high index suspicion. Very few cases of late inborn errors of urea cycle disorders (UCDs) have been reported in the literature. Our case highlights the importance of early diagnosis of UCDs and that outcome can be excellent if treated aggressively. Once identified, adult-onset forms of the UCDs have a good prognosis-largely due to the initiation of preventative measures and earlier recognition of exacerbations.

Keywords: altered mental status; non-cirrhotic hyperammonemia; urea cycle disorders.

Figure 1. Electroencephalogram (EEG) showing diffuse encephalopathy

Figure 2. Magnetic resonance imaging (MRI) of the brain did not reveal any acute abnormality

Figure 3. Urea cycle

OTC deficiency leads to increased orotic acid excretion. AS- argininosuccinate synthetase, AL- Argininosuccinate lyase, CPS- carbamoyl phosphate synthetase I, OTC- ornithine transcarbamylase.