An Unusual Cause of Non-Hepatic Hyperammonemic Encephalopathy

Abstract

Introduction: The clinical syndrome of hyper-ammonemic encephalopathy is most often encountered in the setting of decompensated liver disease. Cases of non-hepatic hyperammonemic encephalopathy are rare and have diverse etiologies. We present an interesting and unusual cause of non-hepatic encephalopathy. Case: A 64-year-old African-American female was admitted with worsening of her baseline mental status and slurred speech that began two days prior to presentation. She denied fevers, recent travel, sick contacts, new medications or any history of liver disease. Her past medical history was significant for hypertension, hyperlipidemia, and transitional cell carcinoma of the bladder which was treated with resection and uretero-sigmoidostomy four years ago. She was afebrile and had unremarkable vital signs. Physical exam was significant for lethargy and slowed neurologic responses. The abdominal exam was normal without signs of chronic liver disease. Lab studies revealed an elevated plasma chloride at 114 mmol/L (ref range: 98-107) and a bicarbonate level of 13 mmol/L (ref range: 22-30) with an anion gap of eight. She had an elevated plasma ammonia of 106 μmol/L (ref range: 0-32). Markers of hepatic synthetic function including bilirubin, prothrombin time and albumin were normal. A serum toxicology screen was negative. A magnetic resonance image of her head was negative for acute or chronic pathology. Ultrasonographic exam showed normal liver morphology without ascites. An EEG showed triphasic waves consistent with metabolic encephalopathy. As the patient had no clinical, biochemical or radiological evidence of hepatic disease to explain her symptoms, we considered that her hyperchloremic acidosis with nonhepatic hyperammonemia could be explained by the presence of the ureterosigmoidostomy. The patient was treated with lactulose and intra-venous hydration. There was rapid improvement on serial neurological exams and the patient was discharged after resolution of metabolic acidosis and hyperammonemia. Discussion: The Mainz Pouch II ureterosigmoidostomy is used for continent urinary diversion. and involves detubularization and spherical reconfiguration of the ureter to create a low-pressure colonic reservoir and ureterosigmoidostomy. Mechanisms causing the hyperammonemia associated with the Mainz Pouch include colonic absorption of nitrogen created by urea-splitting gram negative bacteria in colon. Additionally, the ureterosigmoidostomy provides a porto-systemic shunt, via the rectal veins, for urea to bypass the hepatic metabolism and leads to accumulation of ammonia in the caval system. Treatment of the encephalopathy remains the same as for hepatic causes.