Population-based studies

Organizations that provide social, educational, and training and rehabilitation services are a common source of information on the frequency and nature of associated disabilities in children with MR. These services are not only inexpensive sources of information but, in countries where registration is mandatory for all individuals with one of these disabilities, they are reliable sources for large, population-based studies. However, children who exhibit multiple disabilities are more likely to be referred to these services than are children with only one disability. Thus, it is likely that these services enroll children with particularly severe forms of MR, CP, or epilepsy, resulting in an exaggerated association between these disorders.

Metropolitan Atlanta

The Metropolitan Atlanta Developmental Disabilities Study is a large, population-based, cross-sectional study in which data were collected on 10-year-old children who were born from 1975 through 1977 in the metropolitan Atlanta area and who had one or more of five developmental disabilities: mental retardation (MR), cerebral palsy (CP), epilepsy, visual impairment, and hearing impairment. Data were collected through educational, medical, or social services for children with disabilities.21,22Overall, 15% of children with MR who were enrolled in the Metropolitan Atlanta Developmental Disabilities Study also had epilepsy. The proportion of children who experienced seizures increased with increasing severity of MR:

IQ Proportion with epilepsy
50–70

8%

<50

32%

<20

59%

Of children with MR and coexisting epilepsy, 52% had CP. Of children with MR without epilepsy, only 6% had CP.

Sweden

In Sweden, all individuals with MR are registered to the Board for Provisions and Services to the Mentally Retarded (BPSMR), which supplies services to individuals with MR, whether they reside within institutions or in the community. Forsgren et al.23examined the medical records of individuals reported to have epilepsy who were registered with the BPSMR. Information also was obtained from medical records from departments of neurology, pediatrics, and obstetrics. The study adopted the definition of seizures used by the World Health Organization (“transient dysfunction of part or all of the brain due to excessive discharge of a hyper-excitable population of neurons, causing sudden and transitory phenomena of a motor, sensory, or psychic nature”). Neonatal seizures and all afebrile, unprovoked seizures were included. Epilepsy was considered active if an individual was taking any antiepileptic drug (AED) or if the last seizure occurred not more than 5 years before the prevalence day.

Of the individuals registered to the BPSMR, 20% had epilepsy. Epilepsy was more common in individuals with severe to profound MR than in those with mild to moderate MR:

IQ Proportion with epilepsy
40–70 11%
<40 32%

CP was the most common associated impairment (33.4%). MR was significantly more severe among patients with epilepsy and CP than among those without CP.

The BPSMR was the main source of information in another study, which limited its investigation to 6- to 13-year-old children with MR residing in the city of Goteborg, Sweden.24 The search for children with MR was extended to pediatric clinics, child neuropsychiatric clinics, rehabilitation centers, and electroencephalography laboratories. The frequency of active epilepsy and other associated disabilities on the prevalence day was determined. Epilepsy was defined as the occurrence of two or more unprovoked epileptic seizures and was considered active if the child experienced one or more epileptic seizures during the 5-year period prior to the prevalence day.

The authors reported the proportion of children with MR and active epilepsy to be 26%. The study, consistent with the larger Swedish study,23 showed an increased risk of epilepsy (and CP) with lower IQ:

IQ Proportion with epilepsy Proportion with CP
50–70 15% 14%
<50 45% 59%

In this study, CP was associated with MR and epilepsy in 43% of children.

Aberdeen, Scotland

Goulden et al.5 investigated the cumulative risk of seizures and epilepsy in a prospectively identified cohort of 221 children with MR born between 1951 and 1955 in Aberdeen, Scotland. By age 22 years, 33 (15%) had epilepsy. An additional 16 (7%) had experienced at least one seizure but did not meet the criteria for epilepsy. In children with MR and no associated disabilities, the cumulative risk of epilepsy was only 5.2% at 22 years, as compared with a 38% risk in children with both MR and CP.

Tel Aviv, Israel

Nevo et al.25 reviewed the records of children evaluated in the Tel Aviv Child Development Center between 1981 and 1990. This location serves as primary center for evaluation of all children 0–5 years old who live in the metropolitan area of Tel Aviv and who have one of the following developmental disabilities: speech and language problems, motor and psychomotor delay, and behavior problems. Given the nature of the national health care system in Israel, all children within the geographic area would be referred to the Child Development Center.

The authors classified seizures and epilepsy according to the guidelines for epidemiologic studies on epilepsy issued by the Commission on Epidemiology and Prognosis of the International League against Epilepsy in 1993.26 MR was defined as an IQ of less than 68. Seizures were not the cause of referral to the center. Most of the children (92%) who experienced a seizure were referred to the center after seizure onset.

The study showed a higher risk for seizure in children with more severe brain dysfunctions. The observed cumulative risk of seizures in children by 5 years of age was:

  • 8% in those with MR only
  • 47% in those with CP
  • 68% in those with MR and CP

The results of this study are shown in Figure 1. Interestingly, in this study, the risk of seizure disorders by age 5 years in children referred to the Child Development Center for evaluation of disabilities other than MR or CP was not different from that in the general population.

Kaplan-Meier curves

Cumulative risk of developing unprovoked seizures in 1,946 children referred to the Tel Aviv Child Development Center: effect of presence of mental retardation (MR) and cerebral palsy (CP) on risk of unprovoked seizures. Kaplan-Meier curves. In this figure, the diagnostic groups are mutually exclusive (i.e., MR is MR without CP, etc.).

Clinical series

Bronx, New York

As compared with population-based studies, higher frequencies of epilepsy have been reported among children admitted to the R. F. Kennedy Center (Bronx, NY) for the evaluation of MR, CP, or both.27,28 Medical records of 400 children were reviewed to determine the influence of possible prenatal, perinatal, and postnatal clinical factors on the risk for epilepsy. Children’s birth records, if available, also were reviewed. The study evaluated the frequency of one or more afebrile, unprovoked seizures in these children.

Of children with MR, CP, or both, 30% had experienced at least one unprovoked seizure. The risk of seizures increased with increasing severity of handicap.

In the group with MR, the rate of unprovoked seizures was more than doubled in the group with an IQ of less than 50 as compared to those with an IQ between 50 and 69.

Similarly, in those with CP, the frequency of epilepsy increased from 19% in those with mild motor deficits to more than 50% in those with severe deficits. When the frequency of seizures was evaluated within subtypes of CP, patients with diplegia were unique in that their risk was low overall and within MR strata.

Tampere, Finland

More recently, Eriksson et al.29 studied epilepsy in children with MR registered to a public organization that provides various services for mentally retarded people in the city of Tampere, Finland, and several rural communes. Epilepsy was defined as a “chronic condition in which epileptic seizures tend to occur repeatedly without any detectable extracerebral cause.” At the time that the study was conducted, more than 1,500 clients, 197 of whom were no older than 16 years, were enrolled at the organization.

Of these 197 children with MR, 78 (40%) also had epilepsy. Among the children with epilepsy, 83% had moderate to severe MR (IQ <50), and 17% had mild MR (IQ 50–70). Among individuals with MR in this study, the majority had severe or profound MR (IQ <35).

CP was present in 56% of cases (110 children).

The high rate of epilepsy reported in the study might be explained, in part, by the fact that the authors evaluated only those children registered with the organization. Those with milder forms of MR (and fewer service needs) may not have been included.

Figure adapted from Y Nevo, S Shinnar, E Samuel, et al. Unprovoked seizures and developmental disabilities: clinical characteristics of children referred to a child development center. Pediatr Neurol 1995;13:235-241. 

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 (www.elsevier.com). 

I<
Reviewed By: 
Steven C. Schachter, MD
on: 
Saturday, May 1, 2004