I saw a similar patient 3 years ago. This case report is important – A case of valproate-induced hyperammonemic encephalopathy: look beyond the liver
The patient was admitted to hospital for further investigations and for monitoring with video electroencephalography. In the first 48 hours after admission, her level of consciousness fluctuated. Subsequent tests revealed an elevated venous ammonia level (185 [normal 12–47] µmol/L). Her liver biochemistry was normal; thus, valproate-related hyperammonemic encephalopathy was suspected. Valproate therapy was immediately discontinued, and over the next week, the patient’s level of consciousness, ammonia level and electroencephalograph results returned to normal.
Although the incidence of valproate-related hyperammonemic encephalopathy is unknown, mild and reversible elevations in ammonia have been described in 16%–52% of patients receiving valproate therapy.5 In a case series, asymptomatic hyperammonemia was observed in 52% of patients receiving valproate monotherapy, 55% of those treated with valproate in combination with other anticonvulsants and 8% of patients receiving anticonvulsant regimens that did not include valproate.6 Phenobarbital, and less frequently, phenytoin, carbamazepine and topiramate may exacerbate valproate-related hyperammonemic encephalopathy.5 This condition appears to be more frequent among patients with carnitine deficiency and those with congenital enzymatic defects in the urea cycle.5 Although its pathogenesis is not completely understood, hyperammonemia appears to be the main cause of encephalopathy. Hyperammonemia may arise because of increased renal ammonia production because of reduced glutamine synthesis. The condition may also be due to the inhibition of carbamyl phosphate synthetase or the reduction of hepatic ammonia metabolism owing to decreased carnitine availability, which leads to suppression of fatty acid ß-oxidation.5
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