Post-traumatic epilepsy
Overview
Post-traumatic epilepsy (PTE) is a form of epilepsy that results from brain damage caused by physical trauma to the brain (traumatic brain injury, abbreviated TBI). A person with PTE suffers repeated post-traumatic seizures (PTS, seizures that result from TBI) more than a week after the initial injury. PTE is estimated to constitute 5% of all cases of epilepsy and over 20% of cases of symptomatic epilepsy (in which seizures are caused by an identifiable organic brain condition). It is not known how to predict who will develop epilepsy after TBI and who will not. However, the likelihood that a person will develop PTE is influenced by the severity and type of injury; for example penetrating injuries and those that involve bleeding within the brain confer a higher risk. The onset of PTE can occur within a short time of the physical trauma that causes it, or months or years after. People with head trauma may remain at a higher risk for seizures than the general population even decades after the injury. PTE may be caused by several biochemical processes that occur in the brain after trauma, including overexcitation of brain cells and damage to brain tissues by free radicals. Diagnostic measures include electroencephalography and brain imaging techniques such as magnetic resonance imaging, but these are not totally reliable. Antiepileptic drugs do not prevent the development of PTE after head injury, but may be used to treat the condition if it does occur. When medication does not work to control the seizures, surgery may be needed. Modern surgical techniques for PTE have their roots in the 19th century, but trepanation (cutting a hole in the skull) may have been used for the condition in ancient cultures.
Prevention
Prevention of PTE involves preventing brain trauma in general; protective measures include bicycle helmets and child safety seats. No specific treatment exists to prevent the development of epilepsy after TBI occurs. In the past, antiepileptic drugs were used with the intent of preventing the development of PTE. However, while antiepileptic drugs can prevent early PTS, clinical studies have failed to show that prophylactic use of antiepileptic drugs prevents the development of PTE. Why antiepileptic drugs in clinical trials have failed to stop PTE from developing is not clear, but several explanations have been offered: for example, the drugs may simply not be capable of preventing epilepsy, or the drug trials may have been set up in a way that did not allow a benefit of the drugs to be found (e.g. drugs may have been given too late or in inadequate doses). Animal studies have similarly failed to show much protective effect of the most commonly used seizure medications in PTE trials, such as phenytoin and carbamazepine. Antiepileptic drugs are recommended to prevent late seizures only for people in whom PTE has already been diagnosed, not as a preventative measure. On the basis of the aforementioned studies, no treatment is widely accepted to prevent the development of epilepsy. However, it has been proposed that a narrow window of about one hour after TBI may exist during which administration of antiepileptics could prevent epileptogenesis (the development of epilepsy). Corticosteroids have also been investigated for the prevention of PTE, but clinical trials revealed that the drugs did not reduce late PTS and were actually linked to an increase in the number of early PTS.[2]
Diagnosis
To be diagnosed with PTE, a person must have a history of head trauma and no history of seizures prior to the injury. Witnessing a seizure is the most effective way to diagnose PTE. Electroencephalography (EEG) is a tool used to diagnose a seizure disorder, but a large portion of people with PTE may not have the abnormal "epileptiform" EEG findings indicative of epilepsy. In one study, about a fifth of people who had normal EEGs three months after an injury later developed PTE. However, while EEG is not useful for predicting who will develop PTE, it can be useful to localize the epileptic focus, to determine severity, and to predict whether a person will suffer more seizures if they stop taking antiepileptic medications. Magnetic resonance imaging (MRI) is performed in people with PTE, and CT scanning can be used to detect brain lesions if MRI is unavailable. However, it is frequently not possible to detect the epileptic focus using neuroimaging. For a diagnosis of PTE, seizures must not be attributable to another obvious cause. Seizures that occur after head injury are not necessarily due to epilepsy or even to the head trauma. Like anyone else, TBI survivors may suffer seizures due to factors including imbalances of fluid or electrolytes, epilepsy from other causes, hypoxia (insufficient oxygen), and ischemia (insufficient blood flow to the brain). Withdrawal from alcohol is another potential cause of seizures. Thus these factors must be ruled out as causes of seizures in people with head injury before a diagnosis of PTE can be made.
Prognosis
The prognosis for epilepsy due to trauma is worse than that for epilepsy of undetermined cause. People with PTE are thought to have shorter life expectancies than people with brain injury who do not suffer from seizures. Compared to people with similar structural brain injuries but without PTE, people with PTE take longer to recover from the injury, have more cognitive and motor problems, and perform worse at everyday tasks. This finding may suggest that PTE is an indicator of a more severe brain injury, rather than a complication that itself worsens outcome. PTE has also been found to be associated with worse social and functional outcomes but not to worsen patients' rehabilitation or ability to return to work. However, people with PTE may have trouble finding employment if they admit to having seizures, especially if their work involves operating heavy machinery. The period of time between an injury and development of epilepsy varies, and it is not uncommon for an injury to be followed by a latent period with no recurrent seizures. The longer a person goes without developing seizures, the lower the chances are that epilepsy will develop. At least 80–90% of people with PTE have their first seizure within two years of the TBI. People with no seizures within three years of the injury have only a 5% chance of developing epilepsy. However, one study found that head trauma survivors are at an increased risk for PTE as many as 10 years after moderate TBI and over 20 years after severe TBI. Since head trauma is fairly common and epilepsy can occur late after the injury, it can be difficult to determine whether a case of epilepsy resulted from head trauma in the past or whether the trauma was incidental.
Treatment
Antiepileptic drugs may be given to prevent further seizures; these drugs completely eliminate seizures for about 35% of people with PTE. However, antiepileptics only prevent seizures while they are being taken; they do not reduce the occurrence once the patient stops taking the drugs. Medication may be stopped after seizures have been controlled for two years. PTE is commonly difficult to treat with drug therapy, and antiepileptic drugs may be associated with side effects. The antiepileptics carbamazepine and valproate are the most common drugs used to treat PTE; phenytoin may also be used but may increase risk of cognitive side effects such as impaired thinking.[8] Other drugs commonly used to treat PTE include clonazepam, phenobarbitol, primidone, gabapentin, and ethosuximide. Among antiepileptic drugs tested for seizure prevention after TBI (phenytoin, sodium valproate, carbamazepine, phenobarbital), no evidence from randomized controlled trials has shown superiority of one over another. People whose PTE does not respond to medication may undergo surgery to remove the epileptogenic focus, the part of the brain that is causing the seizures. However surgery may be more difficult than it is for epilepsy due to other causes, and is less likely to be helpful in PTE than in other forms of epilepsy. It can be particularly difficult in PTE to localize the epileptic focus, in part because TBI may affect diffuse areas of the brain. Difficulty locating the seizure focus is seen as a deterrent to surgery. However, for people with sclerosis in the mesial temporal lobe (in the inner aspect of the temporal lobe), who comprise about one third of people with intractable PTE, surgery is likely to have good outcome. When there are multiple epileptic foci or the focus cannot be localized, and drug therapy is not effective, vagus nerve stimulation is another option for treating PTE. People with PTE have follow-up visits, in which health care providers monitor neurological and neuropsychological function and assess the efficacy and side effects of medications. As with sufferers of other types of epilepsy, PTE sufferers are advised to exercise caution when performing activities for which seizures could be particularly risky, such as rock climbing.