A population-based study on epilepsy in mentally retarded children

Purpose: This study presents data on cumulative risk of seizures, cause, comorbidity, and remission of epilepsy among mentally retarded (MR) children followed until the age of 22 years. Methods: A total of 151 MR children were identified at the age of 8 or 9 years by screening four birth cohorts of 12,882 children born from 1969 to 1972 in the Finnish province of Kuopio. Information about epilepsy was gathered longitudinally when children were 9 to 10, 17, and 22 years old. The guidelines for epidemiological studies on epilepsy proposed by the International League Against Epilepsy were followed. Results: By the age of 10 years, 29 of the 151 MR children (19%) had epilepsy. The cumulative risk for epilepsy at 22 years was 21%. The probability of developing epilepsy was increased fivefold in severely MR children compared with mildly MR children, i.e., in 27 of the 77 severely MR children (35%) versus 5 of the 74 mildly MR children (7%). Postnatal causes of mental retardation or association with cerebral palsy increased the risk for epilepsy, especially in the mildly MR children. When these risk factors were not present, the mildly MR children exhibited only a 3% risk for epilepsy, whereas the respective risk was about 10-fold in severe mental retardation. The cumulative probability of epilepsy being in remission for 5 years by the age of 22 was 32%. Conclusions: The cumulative risk of epilepsy varies according to the severity and the cause of the retardation as well as the presence of additional disabilities. The cumulative probability of epilepsy remission tended to increase with age.