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Do Head-Injured Patients Need Prophylactic Anticonvulsants? For How Long?

José A. Menéndez, Nancy R. Temkin,and David W. Newell

BRIEF ANSWER

Background

Each year more than 422,000 people in the United States are hospitalized for head injury (class III data).¹ As a result, tens of thousands of Americans are affected by PTS (class III data).² The estimated number of new occurrences per year ranges from 5,000 to 30,000. According to some reports (some of which predate the use of the Glasgow Coma Scale classification of head injury), ~20 to 25% of all patients who suffer a serious head injury might be expected to experience at least one PTS (class III data)³ (the use of prophylactic AEDs in these reports was variable).

PTSs have been classified into three groups according to the time of their occurrence: (1) immediate seizures, which occur during the first few hours of injury (most occur during the first hour); (2) early seizures, which occur during the first week; and (3) late seizures, which occur more than 1 week after the initial insult (class III data).^3,4

Retrospective analyses by Annegers and collaborators⁵ show that the overall standardized incidence ratio for development of new unprovoked seizures after head trauma is 3.1 (95% confidence interval, 2.5 to 3.8); that is, that those with head trauma have a risk of developing unprovoked seizures that is 3.1 times higher than that of the general population (class III data). This analysis also investigated the relationship between the severity of the injury and the development of posttraumatic seizures. Injuries were classified as mild when accompanied by a loss of consciousness or amnesia lasting less than 30 minutes; as moderate when associated with a skull fracture or with a loss of consciousness or amnesia lasting 30 minutes to 24 hours; and as severe when accompanied by an intracranial hematoma, by a brain contusion, or by a loss of consciousness or amnesia lasting more than 24 hours. The authors found that the standardized incidence ratio was 1.5 after mild injuries, but with no increase over the expected number after 5 years. The standardized incidence ratio was 2.9 after moderate injuries and 17.0 after severe injuries.

The highest seizure rates occur after penetrating injuries. In cohort studies of veterans who sustained penetrating brain injuries in Vietnam, over 53% developed a seizure during the 15 years following injury (class II data).6,7 Approximately 40% of those who developed seizures within 15 years of injury had their first seizure within 4 months after the trauma, 50% within 8 months, and 75% within ~30 months. Despite the relatively high seizure rate after penetrating trauma, patients have a 95% chance of not developing PTS if they remain seizure-free for 3 years after injury (class II data).^4,7

Literature Review

Early Posttraumatic Seizures

The risk of early posttraumatic seizures is related to the severity of the head injury. Jennett⁸ found that the main risk factors are brain contusions and subdural hematomas, which are associated with an incidence of early seizures of greater than 25% (class III data). Annegers et al⁹ described a 19% incidence of early seizures in patients with brain contusions or hematomas (class III data). Epidural hematomas, amnesia that lasts more than 24 hours, or focal neurologic deficits are associated with an increase in the incidence of early seizures of 4 to 10%.⁸

The development of PTS also seems to be influenced by several factors. In terms of patient age, Jennett³ described an early seizure rate of 9% in children under the age of 5 years, as opposed to 4% in older children and adults (class III data). Hahn et al¹⁰ reported a seizure rate of 32% in children with subdural hematomas, but no increase in rate associated with epidural or intraparenchymal hematomas (class III data). They also found that diffuse cerebral edema and a Glasgow Coma Scale score of 12 or less were other important risk factors.

The significance of early PTS is their association with—and predisposition of patients to—late seizures. Even when they follow mild trauma, early seizures are associated with development of late posttraumatic epilepsy in 25% of cases (class III data).³ This rate contrasts dramatically with a late seizure incidence of ~1% for mild head injuries unaccompanied by early seizures, acute hematomas, or depressed fractures (class III data).³ The development of late seizures is not determined by the number or type of early seizures, and late seizures are seen less often in children than in adults (class III data).³ PTSs may occasionally lead to complications, including aspiration pneumonia and status epilepticus. Patients may also suffer major psychosocial sequelae after experiencing a seizure. For example, a temporary loss of driving privileges is mandated in some states.