(687) Acute Severe Hyperammonemic Encephalopathy: A Rare but Life-Threatening Condition

Introduction: Severe hyperammonemic encephalopathy is a medical emergency requiring urgent intervention. We present a case complicated by seizures and severe cerebral edema.

Description: A 70-year-old male with alcohol-related liver cirrhosis, atrial fibrillation and CKD presented with an acute change in mental status over a six hour time span. He had missed several doses of lactulose and rifaximin. Initial evaluation revealed a MELD-Na of 27, lactic acidosis (4 mmol/L), and an ammonia level of 818 umol/L. He was intubated for airway protection. Shortly afterwards, the patient developed persistent seizure-like movements despite multiple doses of benzodiazepines and propofol infusions. CT head done was normal. Repeat ammonia level was 943 umol/L . Continuous renal replacement therapy was urgently started, leading to rapid resolution of the movements and a decrease in ammonia levels to 148 umol/L within six hours. EEG showed generalized periodic discharges that resolved within an hour of starting CRRT. MRI revealed diffuse symmetric cortical restricted diffusion with T2 hyperintensity. Hyperosmolar therapy with hypertonic saline was instituted with neuro imaging showing severe cerebral edema. He remained comatose and despite aggressive treatment, the patient died on hospital day 14 after his family opted for hospice care.

Discussion: Hyperammonemic encephalopathy is a neurologic emergency that can lead to cerebral edema, seizures, coma, and death. Elevated ammonia levels cross the blood-brain barrier, acting as an osmolyte and increasing cerebral blood volume. MRI typically shows bilateral symmetrical cortical abnormalities in the insula and cingulate gyrus, with cytotoxic edema affecting the frontal, temporal, and parietal lobes, while sparing the occipital and perirolandic cortices. The severity of neurologic injury correlates with ammonia levels and the duration of hyperammonemic coma, with levels above 150-200 umol/L linked to an increased risk of cerebral edema. Renal replacement therapy is recommended when ammonia exceeds 200 umol/L in adults, with close monitoring of ammonia levels every 4 to 8 hours until normalization. The prognosis is poor, especially with coma or prolonged hyperammonemia. Prompt management is crucial to prevent cerebral edema, seizures, and intracranial hypertension.