Posttraumatic Seizures and Posttraumatic Epilepsy
Epilepsy develops in a small proportion of head-injured patients. Head trauma caused by street or traffic accidents is increasingly common in infancy, childhood, and adolescence, so posttraumatic epilepsy is an important condition in pediatrics. For many patients, posttraumatic epilepsy is the only serious sequel of their accident, but this supervenes only rarely, considering the high incidence of head injury.
The identification of those patients with head trauma who are at risk for epilepsy is desirable because then practical advice could be given to parents and patients regarding the lifestyle for the children at risk and, later, the choice of a profession and the problems of acquiring a driver’s license. Reliable information is now available about epilepsy after civilian (nonmilitary) injury (Jennett and Teasdale, 1981; Jennett, 1973, 1974), but information about posttraumatic epilepsy in children is still limited (Weiner et al., 1991; Foulon and Noel, 1977; Kollevold, 1976; Jennett, 1973; Hendrick and Harris, 1968). The ability to predict better the occurrence of eventual epilepsy after head trauma also raises a question of the value of and indications for prophylactic treatment of children following head injuries.
The mechanisms underlying posttraumatic epileptogenesis remain unknown. Trauma that results from shearing of the axons could lead to the loss of inhibitory interneurons through anterograde transsynaptic degeneration (Saji and Reis, 1987). The release of aspartate or glutamate following trauma (Faden et al., 1989), the enhancement of reactive gliosis (Nieto-Sampedro, 1988), and the cellular responses to free radical oxidants that result from the release of hemoglobin or iron-containing heme into the brain all may contribute to epileptogenesis (Chandler, 2000).
From a clinical viewpoint, the occurrence of posttraumatic seizures is not a random event. Distinguishing seizures by when they occur relative to the trauma is customary; immediate seizures occur within 1 hour of the trauma (immediate or impact seizures), delayed early-onset seizures are defined as those occurring between 24 hours and 7 days after the trauma, and late-onset seizures supervene later, up to months or years after the trauma. The significance of the timing of the seizures is not the same. Some ambiguity exists with respect to the terminology used in posttraumatic cases. For example, the earliest seizures often remain isolated, and, consequently, they should not be termed epilepsy, a term which is reserved for chronic recurrent seizures. The same applies to some of the early seizures; however, the term early epilepsy is often used for these. Likewise, many authors consider even a single seizure occurring in a patient with an antecedent of significant head injury late epilepsy (Annegers et al., 1980; Jennett, 1973). During the past few decades, several studies have emphasized the different significance of early posttraumatic seizures and late posttraumatic epilepsy (Jennett and Teasdale, 1981; Jennett, 1974), and this distinction is followed in this chapter.
INCIDENCE
The incidence of early seizures varies considerably with the type of injury sustained by the patient and among various series, probably as a result of the lack of agreement on terms, the composition of series, or other methodologic factors. The overall incidence following civilian head injury is between 2% and 2.5% in adults, which rises to 5% for hospitalized neurosurgical patients (Chandler, 2000). The figures are substantially higher in severely brain-injured patients (those with a Glasgow Coma Scale score of 8 or less), reaching 10% to 15% in adults (Temkin et al., 1990; Annegers et al., 1980) and 30% to 35% in children (Hahn et al., 1988). Annegers et al. (1980) found that this high risk was caused by an increased frequency of early epilepsy following severe head injury only. Other authors (Kollevold, 1976; Jennett, 1973; Hendrick and Harris, 1968) have reported that the higher incidence of early seizures in children was almost entirely the result of the greater propensity of young patients compared to adults to develop seizures after mild or trivial trauma. Thus, Kollevold (1976) indicated that frequency of early seizures in children and adults was,
respectively, 4.2% and 0.9% following concussion, 5.4% and 5.8% following contusion, and 21% and 9.2% when an intracranial hematoma was present. The higher incidence of early posttraumatic seizures in children compared with adults can be accounted for by a much higher incidence of immediate (impact) seizures. The findings of Annegers et al. (1980) cast doubt on the reality of an increased frequency of seizures after mild head injury. Another confounding factor may be the high incidence of trivial trauma in childhood, so a coincidence between trauma and the onset of seizures cannot be excluded. Similar discrepancies have been found in various studies with respect to the influence of the type of head injury on the development of early epilepsy. Whereas Annegers et al. (1980) found an incidence of 31% for early seizures following severe trauma and of roughly 1% for mild and moderate trauma, Jennett (1973) did not notice a marked effect of the severity of the trauma on the frequency of early seizures as opposed to its effect on the incidence of late epilepsy. Referral patterns and methodologic differences probably account for such discrepancies.
respectively, 4.2% and 0.9% following concussion, 5.4% and 5.8% following contusion, and 21% and 9.2% when an intracranial hematoma was present. The higher incidence of early posttraumatic seizures in children compared with adults can be accounted for by a much higher incidence of immediate (impact) seizures. The findings of Annegers et al. (1980) cast doubt on the reality of an increased frequency of seizures after mild head injury. Another confounding factor may be the high incidence of trivial trauma in childhood, so a coincidence between trauma and the onset of seizures cannot be excluded. Similar discrepancies have been found in various studies with respect to the influence of the type of head injury on the development of early epilepsy. Whereas Annegers et al. (1980) found an incidence of 31% for early seizures following severe trauma and of roughly 1% for mild and moderate trauma, Jennett (1973) did not notice a marked effect of the severity of the trauma on the frequency of early seizures as opposed to its effect on the incidence of late epilepsy. Referral patterns and methodologic differences probably account for such discrepancies.
The incidence of late posttraumatic epilepsy in children varies from 0.2% to 12%, which is slightly lower than the 1.3% to 15% commonly quoted for adults. The risk of late epilepsy also varies considerably with the severity of head trauma. It is greatly increased with hematoma requiring surgical evacuation, torn dura, and/or posttraumatic amnesia of 24 hours or more. The risk is 12% for severe trauma, 1.6% in moderate trauma, and only 0.6% in mild trauma (Annegers et al., 1980). The last figure is still significantly higher than the incidence of epilepsy in the general population.
Nonaccidental head injuries in infants raise specific problems. According to a recent study (Barlow et al., 2000), the incidence of seizures is much higher than that seen in accidental injuries. Of 44 children seen at one institution, 32 (73%) had early posttraumatic seizures. The average age was 5.9 months. The exact time of occurrence of seizures in such cases is difficult to ascertain, but the peak incidence was seen on the second day of hospitalization and all cases occurred before day 3. The incidence of late-onset epilepsy was also quite high, appearing in 22% of survivors. Six children died, and the outcome with regard to both survival and late epilepsy was strongly correlated with the severity of the injury. The incidence of early status epilepticus was also extremely high (13 patients), and 16 infants had intractable seizures.
EARLY ONSET SEIZURES
Features
Early onset seizures are those that occur during the first week following head trauma. They are mainly concentrated in the first 24 hours, during which period of time at least 50% of cases occur (Snoek et al., 1984; McQueen et al., 1983; Annegers et al., 1980; Hendrick and Harris, 1968). This is due mainly to the very high incidence of impact seizures (Chandler, 2000). As in adults, the incidence of posttraumatic seizures rises with the severity of the head injury. In children younger than 16 years, the proportion is even higher, with 80% of patients having fits within 24 hours of injury (Jennett, 1973). Approximately one-third of those patients with early posttraumatic epilepsy have seizures within 1 hour of the trauma. Most of the early seizures are focal, and, of these, 75% are partial motor attacks, even in children younger than 5 years. The remaining attacks are generalized (Caveness et al., 1979; Maijkowski, 1977; Jennett, 1974). Approximately one-third of patients have only one fit during the first week (Jennett, 1973). However, status epilepticus following head trauma is much more common in children than in adults. Status was observed in 29 (16%) of 177 children, compared with 22 (7.5%) of 288 adults in one series (Jennett, 1973), and the highest incidence (22.1%) was in those children younger than 5 years. Status may cause secondary brain damage resulting from hypoxia or ischemia, but it does not seem to be associated with an increased risk of late epilepsy beyond that associated with any type of early epilepsy (Grand, 1974; Jennett, 1973).
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