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The new epilepsy definition adopted by the International League Against Epilepsy (ILAE) includes patients with one unprovoked seizure with a probability of further seizures, similar to the general recurrence risk after two unprovoked seizures, occurring in a 10-year period. Long-term follow-up of patients diagnosed after a single seizure is needed to assess the applicability of the new epilepsy definition in clinical practice.

Patients with newly diagnosed epilepsy were recruited retrospectively with a minimum follow-up of 10 years. Patients were stratified in two groups depending on the occurrence of one (new definition, ND) or two or more unprovoked seizures (traditional definition, TD) at the time of epilepsy diagnosis and compared for disease characteristics and factors predicting seizure recurrence. The primary outcome was the occurrence of a new unprovoked seizure during follow-up in the ND group. The secondary outcome was the achievement of an early remission in both groups.

Among 1,006 patients with newly diagnosed epilepsy, 152 (15.1%) were diagnosed after a single seizure. Compared to patients diagnosed using the TD, patients diagnosed according to the ND showed a higher proportion of subjects with an abnormal neurologic examination (19.9% vs. 13.7%, p = 0.0504) and with focal seizures (69.3% vs. 60.4%, p = 0.0021). The two samples differed in the presence of at least one of the factors predicting seizure recurrence (focal seizures or abnormal findings in at least one among the following: neurologic examination, electroencephalography [EEG], and neuroimaging) (94.6% vs. 89.1%, p = 0.0376). Long-term recurrence in patients diagnosed with the new definition was 83.6% at 10 years and 89.1% at 15 years. The probability of early remission did not differ between the two groups.

Our results support the applicability of the new epilepsy definition in clinical practice. Individual patient characteristics and a personalized diagnostic approach can justify treatment after a single unprovoked seizure.