Traumatic Brain Injury

Appendix B: Risk of Seizures after Traumatic Brain Injury

Post-traumatic epilepsy (PTE) is defined as recurring seizures transpiring more than 7 days after injury. TBI accounts for 20% of symptomatic epilepsy in the general population and 5% of all epilepsy patients referred to specialized epilepsy centers.21 The incidence of seizures after TBI is21:

• Immediate (<24 hours after injury) = 1-4%
• Early (<1 week after injury) = 4-25%
• Late (>8 days after injury) = 9-42%

Risk of seizures after TBI is usually reported by severity of injury. Annegers, et al., studied a cohort of 4,541 adults and children with mild, moderate, or severe TBI (GCS classification) with no prior history of TBI or epilepsy. Table B-1 shows rate of seizure by years of observation.24

Table B-1. Rate of Seizure by Interval (years) by Injury Severity24

Englander et al., reported that the risk of late post-traumatic seizure was 11.0% during year 1, and 2.7% during year 2 in a population of 647 patients age >16 admitted to a trauma center. At 24-months post-TBI, there was a 13.8% (66/480) likelihood of developing late post-traumatic seizure. Of those with late post-traumatic seizure during the 24-month period, 33.3% (22/66) of the late post-traumatic seizure occurred 8 days to 1 month post-injury, 63.6% (42/66) between 8 days to 6 months post-injury, 80.3% (53/66) between 8 days to 12 months post-injury, and 92.4% (61/66) between 8 days to 18 months post-injury.25

In a National Institute for Disability Related Research (NIDRR) TBI Model System Study, Walker et al. found a rehospitalization rate due to seizure during the first 2 years of 6.1% (436/6671), with 13.7% of respondents indicating that they were told by a physician that they had a seizure in the first 2 years of follow-up. Adjusted odds ratio for risk of seizures in subjects with penetrating traumatic brain injury (PTBI) vs. closed traumatic brain injury (CTBI) was 2.78, adjusted for length of stay, age, sex, substance abuse, and race.26

McGuire et al, published their experience returning US Air Force (USAF) personnel back to flight status after TBI.27 The authors report that the USAF based their medical standards for waiver criteria on Annegers’ 1998 article on seizure risk findings.24 A summary of other agency observation periods after TBI from the article is presented in Table B-2.

Table B-2. Observation minimums for consideration of waiver for aviators due to potential seizure risk by agency and severity of injury. Of note, each agency has slightly different diagnostic criteria defining injury severity.27,28 The US Army also considers loss of consciousness >24 hours to be permanently disqualifying.

The Federal Motor Carrier Safety Administration (FMCSA) Medical Expert Panel’s recommendations on observation periods and certification is based on their own classification of TBI which accounts for dural penetration and seizure risk29:

• Mild head injury (no dural penetration) defined by loss of consciousness <30 minutes.
• Mild head injury without early seizures – Completed the minimum waiting period seizure free (observation period not defined) and off anticonvulsant medication. Normal physical examination, neurological examination including neuro-ophthalmological evaluation, and neuropsychological test. Clearance from a neurologist who understands the functions and demands of commercial driving.
• Mild head injury with early seizures – Completed the minimum waiting period (2 years seizure free and off anticonvulsant medication). Normal physical examination, neurological examination including neuro-ophthalmological evaluation, and neuropsychological test. Clearance from a neurologist who understands the functions and demands of commercial driving.
• Moderate head injury (no dural penetration) defined by loss of consciousness >30 minutes, but <24 hours.
• Moderate head injury without early seizures – Completed the minimum waiting period (2 years seizure free and off anticonvulsant medication). Normal physical examination, neurological examination including neuro-ophthalmological evaluation, and neuropsychological test. Clearance from a neurologist who understands the functions and demands of commercial driving.
• Moderate head injury with seizures – Completed the minimum waiting period (5 years seizure free and off anticonvulsant medication). Normal physical examination, neurological examination including neuro-ophthalmological evaluation, and neuropsychological test. Clearance from a neurologist who understands the functions and demands of commercial driving.
• Severe head injury defined by either dural penetration (including surgical procedures involving dural presentation) or loss of consciousness lasting longer than 24 hours.
• Severe head injury with or without early seizures – disqualified due to high risk for unprovoked seizures and the risk does not diminish over time.

FMCSA also recommends a 5-year waiting period for drivers with “intracerebral or subarachnoid hemorrhage with risk for seizure” and a 1-year waiting period for “intracerebral or subarachnoid hemorrhage with no risk for seizures.”29

Based on the increased risk of late seizures in patients with a confirmed diagnosis of moderate or severe TBI, the LEO Task Group recommends a 2-year restriction period for these LEOs. A 2-year restriction period is also reasonable in the unlikely case where the LEO was diagnosed with a moderate or severe TBI and NOT admitted to an acute care hospital. LEOs who experience immediate, early and/or late seizures should be managed using the criteria in the LEO chapter on Seizures. It is unlikely that the LEO with a penetrating traumatic brain injury (penetration of the dura mater) will be able to be cleared for unrestricted duty due to the lifetime increased risk of seizure.