Epilepsy diagnosis after one seizure remains controversial

PHILADELPHIA -- A new, operational definition of epilepsy may go a long way toward resolving the question of whether epilepsy can be diagnosed and treatment begun after a single seizure or whether two seizures are required. Under the new definition, patients who have had one unprovoked seizure and at least a 50% likelihood of having another seizure in the next 5 years should be considered to have epilepsy that can be treated if the patient wishes.

Limiting a diagnosis of epilepsy only to patients who have had two unprovoked seizures "is too simple". Treatment is appropriate after a single seizure for patients who want to start treatment and have a "medium to high recurrence risk". On the other hand, the decision to start antiepileptic treatment even in patients who have had two unprovoked seizures should not follow a one-size-fits-all approach. Treatment should automatically start only if the two seizures had significant symptoms or occurred within 12 months.

Researchers developed a formula for predicting the risk of seizure recurrence in patients that can guide initiation of therapy. The formula was based on data collected in the MRC Multicenter Trial for Early Epilepsy and Single Seizures (MESS) trial, which compared the efficacy of immediate treatment after a single seizure with deferred treatment (Lancet 2005;365:2007-13). Their analysis showed that number of seizures, EEG abnormalities, and neurologic disorders all boost the risk of recurrence (Lancet Neurol. 2006;5:317-22). The MESS results showed that immediate treatment (using either carbamazepine or valproate in 90% of patients who underwent treatment) had no impact on long-term prognosis, compared with deferred treatment for all patients in the study. In either case, about 68% of the patients remained seizure free by 5 years after their index seizure.
But dividing patients into low-, medium-, and high-risk subgroups based on the scoring system they developed identified patients who received clear benefits from treatment. Both medium- and high-risk patients put on immediate treatment had fewer recurrences than usual-care patients during 1, 3, and 5 years of follow-up. In contrast, low-risk patients never benefited from immediate treatment, even during the first year of follow-up.
An adamant argument against diagnosing epilepsy after one seizure is that a patient who has had just one seizure "may need treatment with antiepileptic drugs if the cause [of the seizure] has a high risk of [triggering] additional seizures". But despite this, several factors may dissuade physicians from making an official diagnosis of epilepsy in patients who have had just one seizure.

A diagnosis of epilepsy has serious social implications, other possible causes of the seizure must be ruled out, and when treatment starts after one seizure there is a risk of erring on the side of overtreatment. It would also be awkward if physicians began to define epilepsy based on single seizures because the existing epidemiologic databases, guidelines, and textbooks are all oriented around the two-seizure model. "If a new definition was adopted, then past [epidemiologic] studies would be irrelevant".

Source: Skin & Allergy News, March, 2009 by Mitchel L. Zoler