These results support the idea that tonic-clonic seizures are an important proximate cause of SUDEP. This information creates a risk profile for SUDEP that may help direct preventative efforts.
We evaluated the risk of unprovoked seizures after febrile convulsions and the factors prognostic of them in a cohort of 687 children who had an initial febrile seizure while residing in Rochester, Minnesota. Overall, children with febrile convulsions had a fivefold excess of unprovoked seizures, and the risk until the age of 25 was 7 percent. The risk ranged from 2.4 percent among children with simple febrile convulsions to 6 to 8 percent among children with a single complex feature--i.e., focal or prolonged seizures or repeated episodes of febrile convulsions with the same illness. For children with any two of the complex features, the risk was 17 to 22 percent, and for those with all three features, 49 percent. The occurrence of subsequent partial unprovoked seizures was strongly associated with all three of the complex features, whereas the occurrence of subsequent unprovoked seizures of generalized onset was associated with the number of febrile convulsions and a family history of unprovoked seizures. These results are consistent with the view that the increased risk of generalized-onset unprovoked seizures reflects a predisposition to both simple febrile convulsions and generalized-onset unprovoked seizures. The association between complex febrile convulsions and partial seizures, on the other hand, may reflect either a causal association or the presence of preexisting brain disease that is responsible for both the complex febrile seizures and later partial seizures.
The incidence of SUDEP in our study was 0.35 per 1,000 person-years. SUDEP was responsible for 1.7% of deaths in our cohort. SUDEP is a rare cause of death in the epilepsy population but exceeds the expected rate of sudden death in the general population by nearly 24 times.
We determined the incidence of seizures due to acute CNS insults for residents of Rochester, Minnesota, U.S.A., from 1935 through 1984. The age-adjusted incidence rates for 1955-1984, the period of most complete case ascertainment, was 39.0/100,000 person-years (United States 1970 population as standard). The age-adjusted incidence was considerably higher in men: 52.0 as compared with 29.5 in women. The 3.6% risk of experiencing an acute symptomatic seizure in an 80-year lifespan approaches that of developing epilepsy. The major causes of acute symptomatic seizures were traumatic brain injury, cerebrovascular disease, drug withdrawal, and CNS infections. Each type of acute symptomatic seizure has age, gender, and time period patterns that reflect the occurrence of the underlying cause.
A population-based cohort of 714 survivors of encephalitis or meningitis between 1935 and 1981 was followed in order to evaluate the risks of unprovoked seizures after CNS infections. The 20-year risk of developing unprovoked seizures was 6.8%, and the ratio of observed to expected cases of unprovoked seizures was 6.9. The increased incidence of unprovoked seizures was highest during the first 5 years after the CNS infection but remained elevated over the next 15 years of follow-up. The type of CNS infection and the presence or absence of seizures during the acute phase of the CNS infection greatly influenced the risks of subsequent unprovoked seizures. The 20-year risk of developing unprovoked seizures was 22% for patients with viral encephalitis and early seizures, 10% for patients with viral encephalitis without early seizures, 13% for patients with bacterial meningitis and early seizures, and 2.4% for patients with bacterial meningitis without early seizures. The 20-year risk of 2.1% for patients with aseptic meningitis was not increased over the general population incidence of unprovoked seizures.
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