Hyperammoniëmische encefalopathie: Zeldzame verwikkeling van valproaattherapie

A 57-year-old woman presented with subacute bradyphrenia and apathy, as well as mild ataxia. Her medical history mentioned epilepsy and she used valproate sodium as an antiepileptic drug. A diagnosis of valproate-induced hyperammonemic encephalopathy (VHE) was made (highest serum ammonia level: 87 µmol/l, normal range: 11-32 µmol/l). The liver function and the serum valproate level were normal. After discontinuation of the valproate medication, a complete recovery was noted and the serum ammonia levels decreased to baseline. VHE should be considered in patients with valproate therapy showing neurological dysfunction, especially bradyphrenia and apathy. In these patients, the serum ammonia levels should be determined. A routine measurement of the ammonia blood levels is not recommended since asymptomatic hyperammonemia is a frequent phenomenon in patients with valproate therapy. In an observational survey of 70 asymptomatic patients taking valproate, an increased serum ammonia was found in 41% of the patients, which is in accordance with the previous reported prevalences in the literature.