Non-convulsive status epilepticus secondary to valproic acid-induced hyperammonemic encephalopathy

Valproic acid (VPA) may induce hyperammonemic encephalopathy. On the other hand, seizure-inducing effects of antiepileptic drugs (AEDs) may be a paradoxical reaction or a result of AED-induced encephalopathy (commonly induced by VPA).

We present the case of a 19-year-old male who developed acute mental status changes consistent with encephalopathy evolving into repetitive seizures with oral automatisms induced by relatively small doses of VPA.

Although serum hepatic enzymes, such as AST and ALT, were normal, serum ammonia concentration was high, i.e. 70 micromol/l (normal range 9-33 micromol/l). Administration of VPA was discontinued immediately after admission. The patient's condition improved during the second week of hospitalization and ammonium levels returned to normal.

In conclusion, although uncommon, a possible induction of non-convulsive status epilepticus by valproate-induced hyperammonemic encephalopathy should be taken into account and properly managed by discontinuation of the drug.