A population-based study on epilepsy in mentally retarded children

Purpose: This study presents data on cumulative risk of seizures, cause, co morbidity, 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 ye ars by screening four birth cohorts of 12,882 children born from 1969 to 19 72 in the Finnish province of Kuopio. Information about epilepsy was gather ed longitudinally when children were 9 to 10, 17, and 22 years old. The gui delines for epidemiological studies on epilepsy proposed by the Internation al League Against Epilepsy were followed. Results: By the age of 10 years, 29 of the 151 MR children (19%) had epilep sy. The cumulative risk for epilepsy at 22 years was 21%. The probability o f developing epilepsy was increased fivefold in severely MR children compar ed 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 re tardation or association with cerebral palsy increased the risk for epileps y, especially in the mildly MR children. When these risk factors were not p resent, the mildly MR children exhibited only a 3% risk for epilepsy, where as the respective risk was about 10-fold in severe mental retardation. The cumulative probability of epilepsy being in remission for 5 years by the ag e of 22 was 32%. Conclusions: The cumulative risk of epilepsy varies according to the severi ty and the cause of the retardation as well as the presence of additional d isabilities. The cumulative probability of epilepsy remission tended to inc rease with age.