Epilepsy is called ‘symptomatic’ when it has a known cause. This may include:
- a head injury
- an infection like meningitis
- the brain not developing properly
- a stroke
- a scar
- a tumour.
A scan, such as a Magnetic Resonance Imaging (MRI), may show the cause.
Some symptomatic epilepsies may happen because genetic conditions such as Tuberous Sclerosis, which causes structural abnormalities in the brain and other organs.
Epilepsy is called ‘idiopathic’ when it is thought to be due to a genetic tendency (which could have been inherited from one or both parents) or due to a change that happens in the person’s genes before they are born.
A genetic tendency to have seizures is likely to be associated with a low seizure threshold. A person’s seizure threshold often plays a key role in whether they will develop epilepsy.
A seizure threshold is our individual level of resistance to seizures. We all have a seizure threshold and any of us has the potential to have a seizure. However some people will be more likely to have a seizure than others.
Our seizure threshold is one part of our genetic make-up which can be passed from parent to child. So the chance of you having seizures may depend partly on whether either of your parents has epilepsy.
If you have a low seizure threshold, your brain is less resistant to seizures. So you are more likely than someone with a high seizure threshold to start having seizures suddenly for no obvious reason than someone with a high seizure threshold
If you have a high seizure threshold you are less likely to have a seizure. However, damage to the brain (for example from a severe head injury or an infection) could lower your seizure threshold; making a seizure more likely.
This is when the cause for a person’s epilepsy has not yet been found, despite investigations.