Silent toxicity: A rare case of 5-fluorouracil-induced hyperammonemic encephalopathy

Hyperammonemic encephalopathy (HE) is a rare but serious neurological condition characterized by an acute alteration in mental status due to elevated serum ammonia levels, occurring in the absence of known liver disease. The build-up of ammonia, a by-product of protein metabolism, in the bloodstream leads to its crossing of the blood-brain barrier, where it acts as a neurotoxin, causing potentially reversible brain damage. Chemotherapeutic agents such as 5-fluorouracil (5-FU) are known to cause drug-induced HE. Our case reports a 63-year-old woman who presented with several episodes of reduced consciousness shortly after 5-FU administration, highlighting the necessity of monitoring serum ammonia levels in patients treated with 5-FU who develop neurological symptoms, and the need for expert consultation in attempting a 5-FU rechallenge.