Encephalopathy and hyperlactatemia as a complication of 5-fluorouracil treatment

Background. There is a wide spectrum of metabolic and toxic disorders that can cause acute encephalopathy in cancer patients. In routine clinical practice, hypoglycemia, vitamin B1 (thiamine) deficit, fulminant liver failure, uremia, severe hypo- and hypernatremia should be primarily excluded. Central neurotoxicity associated with hyperammonemia in patients receiving 5-fluorouracil (5-FU) and oral fluoropyrimidines should be considered in differential diagnosis. In this case, the analysis of the blood acid-base status and the detection of B-type hyperlactatemia can facilitate the diagnosis of the cause of encephalopathy. Case description. We present two cases of hyperlactatemia and encephalopathy in stage IV cancer patients with continuous infusion of 5-FU via a portable infusion pump. Conclusion. Diagnosis of the frequent fluoropyrimidin-related adverse effects, such as myelosuppression, anorexia, diarrhea, mucositis, and palm-plantar syndrome, are routine and mastered by an oncologist at the very beginning of his/her professional activity. Specific fluoropyrimidine-related encephalopathy or hyperlactatemia are difficult to suspect and recognize. We hope our description will be useful to prevent possible diagnostic errors.