Hyperammonaemic encephalopathy presenting as a stroke mimic with normal liver function tests

Hyperammonaemia is a potentially reversible cause of encephalopathy that can mimic focal neurological syndromes. A man in his 60s presented with light-headedness, vomiting and abdominal pain. He developed acute aphasia and right-sided weakness within 24 hours, and although serial CT brain imaging and CT angiography were normal, conscious level deteriorated rapidly, such that he required intubation and mechanical ventilation. MRI brain demonstrated symmetrical basal ganglia T1 hyperintensity. Metabolic investigation identified hyperammonaemia (147 µmol/L). He was treated with lactulose, rifaximin and continuous veno-venous haemofiltration with biochemical and neurological improvement and resolution of neurological deficits. In the absence of overt liver failure, small bowel bacterial overgrowth was considered the most likely cause although potential additional contributory factors were also identified. This case highlights the need to measure ammonia early in otherwise unexplained encephalopathy, even when liver function tests are normal.