Do carbamazepine and phenytoin aggravate juvenile myoclonic epilepsy?

Juvenile myoclonic epilepsy is a frequent form of idiopathic generalized epilepsy that is usually and easily controlled by valproate monotherapy. However, juvenile myoclonic epilepsy is often misdiagnosed, and some drugs, especially carbamazepine and phenytoin, may have an aggravating effect.

To determine the risk of aggravation of juvenile myoclonic epilepsy in patients treated with carbamazepine and phenytoin.

Among 170 consecutive patients with juvenile myoclonic epilepsy (104 female, 66 male) referred between 1981 and 1998, the authors retrospectively found 40 patients (23%) who had received carbamazepine or phenytoin (duration of epilepsy at referral, 1 to 34 years; mean +/- SD, 13.8 +/- 8.5 years; follow-up, 3 to 50 years; mean +/- SD, 16.4 +/- 11 years).

Twenty-three patients (57.5%) experienced aggravation of seizures, whereas 6 (15%) apparently benefited from these drugs. There was no effect in the remaining 11 cases (27.5%). Carbamazepine was prescribed to 28 patients: 19 (68%) had aggravated symptoms, including myoclonic status in two; 4 (14%) were improved, one in association with valproate and one in association with valproate and phenobarbital. Phenytoin was prescribed in 16 cases: 6 (38%) had aggravation and 2 (12%) were improved, including one in association with phenobarbital. Vigabatrin was given in only one case, in association with carbamazepine, and provoked a mixed absence and myoclonic status.

Among commonly prescribed anticonvulsants, carbamazepine appears to have the strongest aggravating potential in patients with juvenile myoclonic epilepsy, whereas the aggravating effect of phenytoin is less prominent. Aggravation was mostly in the form of increased myoclonic jerks.