Application of Recent International Epidemiological Guidelines to a Prospective Study of the Incidence of First Seizures, Newly-Diagnosed Epilepsy and Seizure Mimics in a Defined Geographic Region in Ireland

Abstract

Studies adherent to international guidelines and epilepsy classification are needed to accurately record the incidence of isolated seizures, epilepsy and seizure-mimics within a population. Because the diagnosis of epilepsy is largely made through clinical assessment by experienced physicians, seizures and epilepsy are susceptible to misdiagnosis. Previous epidemiological studies in epilepsy have not captured “seizure mimics”. We therefore sought to quantify the incidence of isolated seizures, epilepsy and seizure-mimics using the International League Against Epilepsy (ILAE) classification system. In this study multiple overlapping methods of case ascertainment were applied to a defined geographic region from January 1 to March 31, 2017 to identify all patients presenting with first seizures (provoked and unprovoked), new diagnoses of epilepsy and seizure mimics. Over a 3 month period, from a population of 542,869 adults and children, 442 potential presentations were identified, and 283 met the inclusion criteria. Radiology databases were the source of the largest number of individual cases (n = 153, 54%), while electroencephalogram (EEG) databases were the source of the highest number of unique-to-source cases (those not identified elsewhere, n = 60, 21%). No single case was picked up in every method of ascertainment. Among the 283 included presentations, 38 (13%) were classed as first provoked seizures, 27 (10%) as first unprovoked seizures, 95 (34%) as new diagnosis of epilepsy and 113 (40%) as seizure mimics. Ten (3%) presentations were indeterminate. We present and apply a rigorous study protocol for investigation of the incidence of first seizures, new diagnosis of epilepsy and seizure mimics in a geographically defined region which is adherent to recently published international guidelines for epidemiologic studies and epilepsy classification. We highlight the challenges in making a diagnosis of new-onset epilepsy in patients presenting with a first seizure using the current ILAE definition of epilepsy, when epilepsy can be diagnosed in situations where the treating physician anticipates the risk of further seizures exceeds 60%.