Epidemiology of Epilepsy in Persons with Intellectual Disabilities

The epilepsies represent one of the most significant groups of conditions that may be associated with intellectual disabilities (ID). There is a general consensus that the incidence (new cases arising in a population in a period of time) and prevalence (the number of people in a population with the diagnosis at a given point in time) of seizure disorders in people with ID are greatly increased compared to the general population, and that the spectrum of epilepsy syndromes and seizure types represented are more refractory and difficult to treat. However, such generalized statements disguise a complex and varied range of presentations, and this chapter will attempt to disentangle some of these relationships in the present state of knowledge. When interpreting the results of studies it is important to remember that not all epileptologists are specialists in the psychiatry of ID, and not all researchers who work in the ID field are epilepsy specialists. Learning disabilities and seizure disorders may be defined or classified in different ways in different studies, and there may be geographical variations in presentation for various reasons. Also, other factors, including developments in prenatal screening, obstetrics, and postnatal care, may yet have a significant impact on the epidemiology of epilepsy in the ID population.