Risk Factors for Post-Traumatic Seizures
The most significant risk factors for post-traumatic seizures include severe traumatic brain injury (GCS 3-8), moderate traumatic brain injury (GCS 9-13), brain contusion with subdural hematoma, skull fracture, loss of consciousness or amnesia lasting more than 24 hours, age over 65 years, midline brain shift ≥5mm, and craniectomy. 1, 2, 3
Major Risk Factors by Severity
Severe Risk Factors
- Brain contusion with subdural hematoma increases risk significantly (standardized incidence ratio of 17.0) 3
- Skull fracture, particularly depressed skull fractures 4, 3
- Loss of consciousness or amnesia lasting more than 24 hours 1, 3
- Age over 65 years 1, 3
- Midline brain shift ≥5mm 4
- Craniectomy has been identified as a risk factor for early post-traumatic seizures 1
- Severe TBI (GCS 3-8) increases risk of seizures by approximately 10 times compared to mild TBI 4
Moderate Risk Factors
- Moderate TBI (GCS 9-13) significantly increases seizure risk (p<0.015) 4
- Neurologic deficit (odds ratio 2-19 across studies) 5
- Signs of basilar skull fracture (odds ratio 10-14 across studies) 5
- Severe headache (odds ratio 3) 5
Other Risk Factors
- Vomiting (odds ratio 3-5) 5
- Post-traumatic amnesia (odds ratio 1.7-8) 5
- Loss of consciousness (odds ratio 2-7) 5
- Posttraumatic seizure (odds ratio 3) 5
- Young age (children under 3 years have higher risk) 6
- Severe cerebral edema 6
Temporal Classification of Post-Traumatic Seizures
- Immediate seizures (within 24 hours): Account for approximately 73.3% of early seizures 6
- Early seizures (within 7 days): Occur in approximately 2.2% of all TBI cases but up to 38% in acute subdural hematoma 2
- Late seizures (after 7 days): Occur in about 2.1% of all TBI cases, but rise to 11.9% in the first year for severe TBI patients 1
Clinical Implications
- The risk of post-traumatic seizures varies significantly based on injury severity and time since injury 3
- Patients with mild TBI have a much lower risk of seizures (standardized incidence ratio of 1.5) with no increased risk after five years 3, 7
- Patients with moderate TBI have an intermediate risk (standardized incidence ratio of 2.9) 3
- Patients with early post-traumatic seizures tend to have worse outcomes, with 53% having a Glasgow Outcome Score ≤3 compared to 19.1% of those without early seizures 6
Monitoring and Imaging Considerations
- Head CT is the preferred initial imaging modality for identifying acute intracranial hemorrhage or mass effect 2
- Continuous EEG monitoring should be considered in patients with depressed mental status disproportionate to their brain injury 1, 2
- MRI is more sensitive for detecting microhemorrhages and diffuse axonal injury but less practical in acute settings 1, 2
Pitfalls and Caveats
- Risk assessment should include evaluation for all risk factors, not just isolated factors 1
- The presence of early seizures does not necessarily predict late seizures in all cases 1
- Antiepileptic prophylaxis is not routinely recommended for primary prevention of post-traumatic seizures 1, 2
- If antiepileptic medication is used, levetiracetam is preferred over phenytoin due to better tolerability 2
- Phenytoin specifically should be avoided as it is associated with excess morbidity and mortality in patients with subdural hematoma 2