Case Presentation: We present a case of a 55-year-old Caucasian woman with a history of hypothyroidism, anxiety, depression, burns affecting 70% of body area (sustained in a motor vehicle accident 4 months before this admission), and recent COVID-19 infection, who presented for altered mental status. She was noted to be less conversive than baseline and had been recently treated with a course of ceftriaxone for a urinary tract infection (UTI) at her skilled nursing facility. In the emergency department, she was also found to have an acute kidney injury and signs of persistent UTI. Computerized tomography (CT) imaging of the head was negative for any acute intracranial process. CT of the abdomen/pelvis revealed fatty liver but her liver enzymes were within normal limits. Subsequently, her blood cultures grew multidrug-resistant Acinetobacter and coagulase-negative Staphylococcus in addition to her urine culture growing Pseudomonas. She was treated with broad-spectrum antibiotics. However, she remained altered with poor oral intake. Workup for encephalopathy was unrevealing aside from an elevated ammonia level of 275 µ/dL. She was started on lactulose with only minimal improvement in ammonia levels. She subsequently began to experience recurrent episodes of hypoglycemia and a nasogastric feeding tube was placed for tube feeds. Once enteral feeds were resumed, ammonia level quickly normalized, and lactulose was subsequently discontinued without recurrent encephalopathy. By day of discharge, she returned to her baseline mental status. After discussion with family, a percutaneous endoscopic gastrostomy tube was placed and she continued tube feeds on discharge.
Discussion: Ammonia is continually produced during metabolism. It crosses the blood-brain barrier readily and leads to cerebral dysfunction causing a spectrum of neuropsychiatric and neurological symptoms. Under normal circumstances, the urea cycle eliminates ammonia efficiently through a highly integrated system which keeps levels below 50 µ/dL. Most cases of hyperammonemia are due to liver disease as hepatic conversion of ammonia to glutamine prevents entry of high levels of ammonia into the systemic circulation. In hypercatabolic states as in this burn patient with prolonged poor oral intake, encephalopathy occurs when the ammonia load is excessive. Other less common etiologies of hyperammonemia occur when portal blood from the intestine bypasses the liver or the urea cycle functions poorly due to inborn errors of metabolism. In the absence of liver dysfunction, etiological diagnosis may be missed or delayed.
Conclusions: In patients with poor nutrition, protein catabolism can overwhelm the urea cycle leading to elevated ammonia levels and subsequent toxic metabolic encephalopathy. Early diagnosis and prompt treatment must be instituted to prevent long-term neurological damage or fatality.