Epilepsy is said to occur when an individual has two or more unprovoked seizures. It appears sometime during life in 1% of the general population. Hauser and Hesdorffer3 estimate that 0.4–0.8% of children will have epilepsy by the age of 11 years. Early studies found that the incidence of childhood epilepsy in industrialized populations was 50 to 100 per 100,000 population.4 More recent studies, however, have found the overall incidence of childhood epilepsy to be 40 per 100,000 children per year.5,6 The incidence of epilepsy is highest in the first year of life (120/100,000) and falls dramatically between 1 and 10 years of age to 40–50 per 100,000. It then drops even further in the teenage years, to 20 per 100,000.
A critical issue when considering epilepsy and cerebral palsy is whether the epilepsy is idiopathic or symptomatic. Idiopathic epilepsy appears suddenly with no underlying cause and frequently involves generalized seizures. It often is characterized by:
In contrast, symptomatic epilepsy may be the result of an acquired insult or an indication of an underlying process, such as abnormal neuronal development and migration in the prenatal period. It also may result from a problem within the developing brain due to intrauterine disease. Symptomatic epilepsy is commonly seen in those with cerebral palsy. Its characteristics often are the opposite of those of idiopathic epilepsy:
The seizures of symptomatic epilepsy often are focal but can be generalized.
In most large studies of people with epilepsy only, 20% of seizures are considered to be symptomatic and the remainder either idiopathic (30%) or cryptogenic (50%; no identifiable underlying etiology, and the epilepsy does not take the form of one of the specific idiopathic syndromes).7
It would seem intuitively obvious that most epilepsy accompanying cerebral palsy would be symptomatic, but no sufficiently large or notable studies of seizure type and linkage with a specific area of motor deficit exist.
Because we expect children with focal motor deficits to experience a focal epilepsy and those with quadriplegia caused by global brain abnormalities to have generalized seizures, we should be able to refer to population-based studies of epilepsy to discern the frequency of seizure type. According to the literature, generalized seizures account for 45% of all seizure types, whereas focal seizures with secondary generalized seizures are present in 55% of cases.5,7 Unfortunately, these studies note the presence of only “neurologic abnormality” rather than the specific type of problem (e.g., cerebral palsy, visual impairment, deafness). Therefore, it is not possible to determine the number of children with epilepsy who also have cerebral palsy (and which cortical area is involved) using population-based studies of epilepsy alone.
The importance of a genetic predisposition to epilepsy in those also having cerebral palsy is impressive. The National Collaborative Perinatal Project demonstrated that the incidence of cerebral palsy in offspring was associated with a maternal history of epilepsy.8
The incidence of nonfebrile seizures in offspring of women with epilepsy but without cerebral palsy was associated with a history of motor deficits in siblings, implying a shared genetic susceptibility to epilepsy and cerebral palsy.
The frequency of epilepsy is elevated in first-degree relatives of children with cerebral palsy, implying that genetic factors play an important part in both of these chronic disabilities. When epilepsy was reported in a first-degree relative of a child with cerebral palsy and mental handicap, Curatolo et al.9 reported that epilepsy was 17 times more frequent in those children than in normal controls. Asku10 described a cohort of children with cerebral palsy and epilepsy in whom 16% of first-degree relatives also had epilepsy, as compared to 8% of first-degree relatives of the normal controls. Others have found similar results.3,11
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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