Incidence and clinical characterization of unprovoked seizures in adults: A prospective population-based study

In a population-based prospective study of epileptic seizures in adults aged greater than or equal to 17 years, we identified 563 patients with possible seizures in a period of 34 months. Seizures were unprovoked in 160 patients, an incidence of 56 in 100,000 person-years. There was no difference in incidence between sexes. Age-specific incidences of unprovoked seizures increased sharply in men from age 60 years and in women from age 70 years. The incidence of unprovoked seizures in those aged greater than or equal to 65 years was 139 (men 166, women 116). The cumulative incidence of unprovoked seizures between the ages of 17 and 84 years was 4.6%. The proportion with an identified presumptive cause for unprovoked seizures increased with advancing age. A presumed etiology was identified in 77% of persons aged greater than or equal to 60 years. Stroke was the most common etiology, detected in 30% (incidence 16) and in 45% at ages greater than or equal to 60 years. Tumors were detected in 11% (incidence 6) and Alzheimer's disease was detected in 7% (incidence 4). Eighteen percent of patients were demented. Unprovoked seizures were partial in 68% of cases (incidence 38), and generalized in 16% (incidence 9). Another 13% of patients had generalized seizures, but seizure onset was not witnessed (incidence 7). In 16%, there was a delay of greater than or equal to 1 year from the first unprovoked seizure to initial diagnosis.