Research has shown that traumatic brain injury carries a high risk of seizure in the weeks / months after the event. However the length of time this risk lasts was previously not known.

A team from Aarhus University Hospital, Denmark, recently examined the long-term risk of epilepsy, by analysing data from 1.6 million people who were born in Denmark between 1977 and 2002.

When scientists talk about the risk of a specific outcome after a particular 'event,' they use the term 'relative risk'; because they have to take into account the possibility that the outcome would have occurred anyway. Relative risk here is a ratio between the probability of epilepsy developing after a head injury, and the probability that the person would have developed epilepsy without the injury. If the relative risk is 2, it is twice as likely that epilepsy will develop after an injury.

During the study period, approximately 78,500 people had a traumatic brain injury and an estimated 17,500 people developed epilepsy.

In the brain, nerve cells must receive a minimum number of signals before they become active themselves and pass the signal on. The researchers, therefore, created neuron 'stripes' by grouping nerves together via their axons, and then investigated whether the width of the stripe (number of axons) would affect how well it could pass signals on.

The relative risks for epilepsy were found to be 2.22 after mild brain injury and 7.40 after severe brain injury. Skull fracture also increased the risk by 2.17-fold.

Ten years after brain injury, the relative risks still 1.51, 4.29, and 2.06 for mild brain injury, severe injury, and skull fracture, respectively.

The researchers found that the likelihood of seizures was directly related to the age at which the injury occurred, and that it was especially high for those who were older than 15 years of age. Higher risks were also seen in patients with a family history of epilepsy, and women were more likely to experience seizures than men.

This study provides useful information about the risk of epilepsy after brain trauma. This will enable doctors to make more informed decisions in the immediate treatment and long-term follow-up of patients with head injury.

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