Epidemiology of Post-Traumatic Epilepsy after Mild Traumatic Brain Injury

In the context of mild traumatic brain injury (mTBI), understanding the occurrence and outlook of post-traumatic epilepsy (PTE) reveals a complex clinical scenario. Recent studies have shown that although the risk of developing PTE is lower after mTBI than after moderate or severe traumatic brain injury (TBI), several key factors can significantly increase this risk. These risk enhancers include the presence and kind of intracranial hemorrhage, the occurrence of early post-traumatic seizures (EPTS) within the initial week following the injury, and a history of alcohol misuse.

The manifestation of seizures after mTBI can differ, with some individuals developing PTE while others experience no lasting effects. A noteworthy aspect is the presence of subclinical seizures, which are only detectable through EEG monitoring, suggesting a more complex underlying mechanism of post-traumatic seizures in cases of mTBI.

Annually, over 2% of the population in England and Wales seek emergency care for head injuries, a significant number of whom are children. Around 20% of these incidents involve a skull fracture or signs of TBI, with about 15% necessitating hospital admission. The spectrum of seizures post-TBI ranges from immediate concussive episodes to early seizures within a week and late epileptic seizures occurring more than a week after the injury. Notably, concussive seizures, first identified in Australian football players, differ from tonic-clonic seizures and are thought to include elements of primitive reflexes, typically not leading to later epilepsy.

In a study of 1000 patients with head injuries in Oxford, early seizures were noted in 4.5% of cases, often associated with skull fractures or intracranial hemorrhage. Another study found early seizures in 2.4% of 4232 cases initially deemed mild head injuries based on the Glasgow Coma Score (GCS), with further imaging often uncovering significant hemorrhage, suggesting more severe injuries. A large-scale study from the National Trauma Data Bank in the USA reported early seizures in just 0.4% of cases but identified a significant 7% mortality rate and a higher incidence among Afro-Caribbean patients and those with a history of alcohol misuse.

Research into subclinical seizures detectable by EEG has uncovered important insights, such as Vespa’s study showing that 22% of patients with moderate to severe TBI experienced mostly subclinical seizures. Similar findings were reported in children with TBI, where 16.1% monitored had subclinical seizures, which correlated with worse TBI outcomes, underlining the recommendation for continuous EEG monitoring in suspected seizure cases following moderate to severe TBI.

Epilepsy, more broadly, is influenced by previous TBI in about 5% of new epilepsy cases and 20% of existing cases. Young adults and the elderly are particularly at risk of developing seizures post-TBI, with the highest risk linked to penetrating brain injuries, evidenced by over half of Vietnam veterans with such injuries developing epilepsy. Research on TBI patients in trauma units, which tends to focus on more severe injuries, supports the gradation of risk from mild to severe injuries. This risk correlation was highlighted by Annegers, who classified TBI into mild, moderate, and severe categories, associating severity with the increasing risk of seizures over 20 years.

Yeh and colleagues, using the ICD-9-50 definition of concussion, expanded on the risk factors by comparing nearly 20,000 emergency department patients with head injuries to a control group. They underscored the heightened risk of epilepsy in cases with more severe brain injuries, emphasizing the importance of a nuanced understanding of TBI severity in relation to the risk of developing PTE, considering factors such as a history of alcohol misuse and specific types of brain injury.

Literature – further reading:

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