Epilepsy - What is It and Why - Fact Sheet

Epilepsy has a close relationship with brain injury. Epilepsy can cause neural damage by itself and is a risk factor for acquiring a traumatic brain injury through a fall or violent convulsion. Epilepsy can also be caused by a brain injury and, confusing things even more, anti-convulsant medications prescribed for epilepsy may also be prescribed to people with a brain injury to help stabilise unstable mood states (known as “emotional lability”).

“Epilepsy” is the term commonly used for a seizure disorder due to a disorder in brain functioning. One seizure alone is not enough for a diagnosis of epilepsy and may be a once-off occurrence. There are also other conditions, including an elevated temperature or chemical toxicity, which can cause seizures but which do not result in a diagnosis of epilepsy.

Epilepsy is categorised into primary and secondary. In primary epilepsy, there is no discoverable abnormality in the brain and therefore no known cause. In secondary epilepsy the seizures are caused by an abnormality in brain tissue which can be found by a CT or MRI scan. A brain injury can lead to secondary epilepsy.

A seizure (also known as a “fit” or “convulsion”) is a temporary alteration in brain function expressing itself in a changed mental state, tonic or clonic movements and various other symptoms. Seizures are due to temporary abnormal electrical activity of a group of brain cells. A seizure can be categorised as absence (also known as “petit mal”) or tonic-clonic (“grand mal”). Absence seizures look like “spells”: A person having an absence seizure may have a blank or distant expression on their face and may even move without intent from place to place. An absence seizure may only last for seconds and should not be immediately dangerous unless the individual is in a situation, such as driving or cooking, where inattention could lead to a dangerous situation developing. In contrast a tonic-clonic seizure is the more recognisable “fit”. Tonic refers to muscle tone, and describes all the muscles in the body going rigid at once. Clonic refers to the muscles contracting and relaxing in rapid succession and describes convulsions that follow the tonic phase.

Seizures can also be categorised as general or partial. A general seizure begins on both sides of the brain. Full convulsions or brief staring episodes are often the result. A partial seizure originates in one region of the brain. In a simple partial seizure, the seizure related brain messages remain localised so that one experiences a feeling, sensation, movement, or other symptom without any change in the level of awareness. Some may suddenly become confused, fumble, wander or repeat inappropriate words or phrases.

There is frequently an “aura” before a seizure, which can include sensory hallucinations, dizziness or light-headedness, feelings of panic or déjà vu. On the other hand, there may be no warning at all. Recognising and acting upon pre-seizure sensations can be an important technique for preventing serious physical injury.

One particular sub-type of epilepsy is Temporal Lobe Epilepsy. The effects of temporal lobe epilepsy are varied, but can include intense emotions, sensory hallucinations and altered mental states while conscious. It has been rumoured that the early twentieth century Russian composer Dmitri Shostakovich (1906 – 1975) had temporal lobe epilepsy arising from a metal shrapnel fragment which was embedded in his brain during the First World War. When he tilted his head to one side, the fragment would press upon his temporal lobe and he would hear melodies which he would use in his compositions.

The uncontrolled excitability of neurons that lead to seizures can cause long-term structural and functional changes in the nervous system and brain. In particular, seizures result in damage to the hippocampus and the amygdala, two regions responsible for memory and emotion among other functions. The causes of these changes are only poorly understood.

Brain injury caused by persistent and highly repetitive seizures is associated with the production of toxic chemicals within the brain as a result of the excessive neural stimulation. The damage caused by these toxins may include the destruction of inhibitory neurons, leading to more epilepsy.
Brain injury associated with individual seizures can be caused either by head trauma during a severe tonic-clonic seizure or as a result of a fall caused by a seizure, or can be a hypoxic injury associated with hyperventilation and, thus, insufficient oxygen in the blood.

According to American studies, a quarter of all people with moderate to severe brain injury will develop epilepsy. Injuries that cause bleeding inside the brain are the riskiest. There is usually a three month or greater delay between the injury and the onset of the first seizure, but this time can vary widely and can run to years. The longer the time between the injury and the onset of seizures, the greater is the chance of developing full epilepsy.
The mechanism by which epilepsy is caused by a brain injury has only been recently understood: Following an injury, the brain trains to rewire itself. Neurons can not fully recover, and new neurons can not be built, but neurons can form new connections to other neurons. This process is called “plasticity” and is crucial to recovery from a brain injury. Unfortunately, plasticity is not perfect. A neuron may make a connection in the wrong place, or may make a connection which is too sensitive and overly excitable. Both these errors may lead to epilepsy.

Anti-convulsant medications are given to head trauma patients as a precautionary measure – a seizure may be caused by pressure on the brain, and if one occurs while a patient is in critical care can have a serious negative effect upon outcome. This medication is usually tapered off and removed during the course of rehabilitation. Recent research has suggested that new anti-epilepsy medications may actually be able to prevent epilepsy if given during the rehabilitation process, but this research is still in its infancy and no conclusive results are available yet.

Epilepsy caused by a brain injury does not usually start with a severe tonic-clonic seizure. It may begin with absence seizures categorised by memory loss, attention problems or other subtle symptoms that may not be recognised as a seizure.

1. Effect of Epilepsy on neural circuits
http://www.cerebromente.org.br/n16/question/epilepsia.html
2. Epilepsy Queensland
http://www.epilepsyqueensland.com.au/
3. Epilepsy Action of Australia
http://www.epilepsy.org.au/
4. Epilepsy.com: Epilepsy and seizure information for patients and health professionals
http://www.epilepsy.com
5. Temporal lobe epilepsy
http://www.epilepsy.com/epilepsy/epilepsy_temporallobe.html