Age of onset

The age of onset of epilepsy is earlier in children with mental retardation (MR) or cerebral palsy (CP) than in children without these conditions. Among children who present with a first unprovoked seizure before age 20, this first seizure occurred earlier than age 3 years in only 27%.43 In the study of new-onset epilepsy (defined as two or more unprovoked seizures) in children younger than 15 in Connecticut, 14% experienced their first episode before age 1 year.40 This contrasts with age of onset of epilepsy in a prevalence cohort of people of all ages with MR and epilepsy, in which almost 27% of patients with MR experienced seizures during the first year of life.23 Seizures occurred at between 1 and 7 years in another 59% of patients. Overall, the first seizure occurred before age 17 in 84% of individuals.

In the population-based series from Goteborg, Sweden, of children between ages 6 and 13 years with active epilepsy and MR, the median age at seizure onset was 1.3 years.37 Children with severe MR had a significantly earlier seizure onset (median age, 0.8 years) than those with moderate MR (median age, 3.1 years). The onset of epilepsy occurred before age 1 year in 43% of cases. This contrasts with a population-based study of all childhood epilepsy in Sweden, in which only 27% of all children with active epilepsy experienced onset before age 1.44

In a series from the Tampere region of Finland, 54% of children with MR and epilepsy experienced onset of epilepsy before the age of 1 year, and 85% had experienced their first seizures by the age of 3 years.29 Among those who experienced the first seizure in the first year of life, 71% also had CP, whereas CP was present in only 39% of patients whose first seizure occurred later.

Zafeiriou et al.34 compared two series of patients with epilepsy (with and without CP) whose epilepsy had been diagnosed according to identical criteria. The age of onset of epilepsy was significantly earlier in the group with CP, occurring in the first year of life in 71% of children with CP as compared to 5.3% of children without CP.

Among children with intractable epilepsy with onset before the age of 13 years, the first seizure occurred significantly earlier (mean age 2.1 years) in mentally retarded children (IQ <70) than in children with an IQ greater than 70, in whom the mean age of onset of epilepsy was 5.0 years.45

Although children with MR experience an earlier onset of epilepsy, onset clearly is not restricted to the very young. The risk of developing epilepsy remains elevated in children with MR at least through the second decade of life.5,27,28 Goulden et al.5found an increasing cumulative risk for epilepsy:

Age Risk of epilepsy
5 years 9%
10 years 11%
15 years 13%
22 years 15%

Among those with MR only, the risk did not differ between those with severe MR and moderate MR. The cumulative risk was highest in the group of children with MR and CP. In all groups, new cases appeared in the second decade of life.

Similarly, the clinic-based series from the Children’s Evaluation and Rehabilitation Center in the Bronx, New York, also found new cases of epilepsy occurring well into the second decade of life.5,27,28

As do children with MR, children with CP develop epilepsy in early childhood, 39%42 to nearly 70%34 of such children experiencing their first seizure in the first 12 months of life. The median age of onset of epilepsy in children with associated CP (18 months) was substantially younger than in children with epilepsy without CP (84 months). In the study by Hadjipanayis et al.,33 the likelihood of seizures in the first year of life was linked to the severity of the CP:

CP classification Onset of epilepsy in first year
Tetraplegia 58.0%
Diplegia 29.6%
Hemiplegia 19.6%
No CP 6.3%

Seizure types and frequency

Epilepsy in children with MR is characterized by:

  • multiple seizure types
  • intractable seizures
  • frequent seizures

In the Atlanta Developmental Disabilities Study,22 25% of children with profound MR had multiple seizure types, versus none of the children with mild MR. In the population-based study from Goteborg of children with MR and epilepsy, 46% of the children exhibited more than one seizure type.37 In this study, 30% had two types and 16% had three or more. The most common seizure types were tonic-clonic, myoclonic, atypical absence, and partial complex seizures.

In children with epilepsy, MR and CP are factors that predict therapeutic resistance to AEDs. In a study of children with MR and epilepsy, 27% of children with MR23 experienced more than 50 seizures, and 11% experienced more than 300 seizures the year before they were included in the study. Among mentally retarded patients with epilepsy, 5% were being treated with AEDs and, of these, more than 33% were on two AEDs, 15% on three, and 1% on four AEDs. Huttenlocher and Hapke45 found that among children with seizures refractory to medical therapy, 61% of children had mild to moderate MR.

Hosking et al.46 evaluated the frequency of MR or CP in children with epilepsy who were seen at a pediatric center. As compared to those without any neurologic disability, children with CP or severe intellectual impairment had three times the number of admissions to a hospital because of difficulties with seizure control and four times the number of changes in medication for lack of control or the occurrence of side effects. Children with neurologic abnormality also were more likely to remain on two or more AEDs (50%) as compared to those without such abnormality (34%).

Children with CP were more often on AED polytherapy than were children without CP.29 Zafeiriou et al.34 found that 53% of patients with epilepsy and CP were on polytherapy, as compared to 30% of those without CP.

High seizure frequency also was observed in children with CP (52%) as compared to those without CP (31%).34 In addition, children with CP were more likely to experience prolonged seizures and to require multiple medications to control those seizures.29 The increased susceptibility of children to very prolonged seizures, including status epilepticus, is well known.2,47–53 Children are also at increased risk for recurrent episodes of prolonged seizures.53–55

Adapted from: D'Amelio M, Shinnar S, and Hauser WA. Epilepsy in children with mental retardation and cerebral palsy. In: Devinsky O and Westbrook LE, eds. Epilepsy and Developmental Disabilities. Boston: Butterworth-Heinemann; 2001;3–16. With permission from Elsevier (