The Epidemiology of Posttraumatic Epilepsy

Population Based Epidemiology of Epilepsy After Traumatic Brain Injury

With the new definition of epilepsy proposed by the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE), epilepsy is a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures.^[11,12] The definition of epilepsy requires the occurrence of at least one epileptic seizure.^[12] Thus, a single, late, unprovoked seizure in a person with a structural TBI fulfills the diagnostic criteria for epilepsy. In accordance with this, the risk of recurrent late seizures 2 years after TBI was 86% in a study of 63 moderately-to-severely head-injured adults who developed late posttraumatic seizures.^[13]

The most important and constant finding when studying posttraumatic epilepsy is that the severity of brain injury is associated with the risk of subsequent epilepsy.^[8,14] In a follow-up study from Denmark, the authors followed more than 1.6 million children and young adults for up to 30 years after TBI. Relative to no brain injury, the relative risk (RR) of epilepsy was twice as high after mild TBI (RR = 2.22, 95% confidence interval [CI]: 2.07–2.38); 7 times higher after severe brain injury (RR = 7.40, 95% CI: 6.16–8.89); and twice as high after skull fracture (RR = 2.17, 95% CI: 1.73–2.71).^[14] The risk of epilepsy was highest shortly after the TBI, but remained increased for more than 10 years after TBI (Fig. 4). The risk was highest in persons older than 15 years of age at the time of TBI. The relative risk of posttraumatic epilepsy was higher in women than in men, and the risk was higher in people with a family history of epilepsy.^[9]

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Figure 4.

Relative risk of epilepsy after brain injury in Denmark, 1977–2002.¹⁴

A study from Olmsted County, Minnesota, identified 4,541 children and adults with TBI occurring between 1935 and 1984.^[10] The standardized incidence ratio for epilepsy compared with the background population was 1.5 (95% CI: 1.0–2.2) after mild TBI, 2.9 (95% CI: 1.9–4.1) after moderate TBI, and 17.0 (95% CI: 12.3–23.6) after severe TBI.^[15] The authors identified brain contusion with subdural hematoma, skull fracture, loss of consciousness or amnesia for more than one day, and an age of 65 years or older as risk factors for epilepsy.^[8]

A population-based U.S. study followed 2,118 persons hospitalized with TBI for 3 years and determined the cumulative incidence of posttraumatic epilepsy.^[15] After adjusting for the significant loss to follow-up (55% at 3 years), they found a risk of 4.4 per 100 persons for mild TBI, 7.6 per 100 persons for moderate TBI, and 13.6 per 100 persons for severe TBI. A history of psychiatric depression increased the risk of posttraumatic epilepsy.^[15] A study from Sweden found that in children with TBI, eight (7%) of 109 developed immediate seizures and 12 (11%) developed epilepsy. Of these 12, 5 had had immediate seizures.^[16]