What is the link between seizures and dementia?

How common are epileptic seizures in dementia? Who is most at risk of having them? What do these seizures look like? What effect do they have on how someone’s memory changes over time?

These are the questions that I have been researching since starting my PhD in 2016. I'm a student funded by Alzheimer’s Society as part of the University of Exeter doctoral training centre.

What do we know about seizures and dementia?

People with dementia are at risk of having epileptic seizures. We’ve known this for a long time – it was described by Alzheimer himself in 1911.

However, how common they are remains unclear. This is because epileptic seizures can often be subtle. 

There are two common types of epileptic seizures:

Generalised tonic-clonic seizures

Most of us are familiar with the kind of epileptic seizures we see on TV or in films. People become unresponsive, they fall to the ground, become stiff and their whole-body shakes in a convulsion.

Generalised tonic-clonic seizures are hard to miss. But this is not what most epileptic seizures look like. 

Focal onset seizures

Most epileptic seizures in people with dementia are known as focal onset seizures. These can involve brief periods of increased amnesia or unresponsiveness. We see involuntary repeating movements, often of the hands and arms, or of the face (chewing, lip-smacking or swallowing).

Understandably, the latter are more easily missed, especially as the person affected will often quickly be back to normal afterwards.

Who might be affected by seizures?

For a long time, researchers believed epileptic seizures occurred only in people who had long been diagnosed with dementia. It was thought they were a reflection of how much the brain had changed and shrunk because of it. 

However, more recent research has suggested that seizures can occur early-on in Alzheimer’s disease. In some people, seizures may happen even before memory problems become apparent.

As part of my research, I recruited people from the local memory clinic here in Exeter. We asked them questions about epilepsy.

It quickly became clear that most people don’t know that having dementia, particularly Alzheimer’s disease, can increase your risk of seizures.

In our group, around 1 in 8 patients with dementia described episodes which we believe could have been epileptic seizures.

We interviewed our participants one year later and found that those who had described having had epileptic seizures previously performed less well on memory tests than those who showed no evidence of epilepsy. 

Why do people with dementia develop seizures? 

Ultimately, anything that changes the structure of the brain can cause seizures. 

This happens for some people after a stroke, a head injury, or with a brain infection like meningitis. A similar problem is happening in the brain in dementia. As cells in the brain die and the brain shrinks this can lead to epilepsy. 

In addition, we know that two proteins that build up in the brain of people with Alzheimer’s disease – amyloid and tau – affect how the brain’s nerve cells communicate with each other.

Sometimes these nerve cells can become 'hyper-excitable', meaning they can behave uncontrollably, causing epileptic seizures.

Can seizures be managed in people with dementia?

There is good news. There are medicines that are effective at reducing, and hopefully stopping, epileptic seizures.  

If you think that you or someone you know with dementia may be having epileptic seizures, you should tell a doctor. They might want to perform some extra tests and may want to start some extra medicines to treat this problem. 

What we don’t know yet is whether starting treatment for epilepsy might help to slow down dementia and whether it might help keep people’s memory function better for longer.

When is anti-seizure medication typically prescribed?

Anyone can have an epileptic seizure, but most people who have a single seizure will not have any more. As a result, doctors do not usually prescribe anti-seizure medicines in someone after a single seizure.  

While they can be distressing to witness, people who have a seizure typically return to their normal selves soon afterward with no long-term effects. 

However, doctors are likely to look for causes as for why a single seizure may have happened.  

In people with dementia, the fact that they have dementia can be the ‘why’, but other causes should also be considered – including stroke, head injury, and infections.

If someone has a second seizure it suggests they have epilepsy, so starting anti-seizure treatments would be appropriate. Usually this involves a discussion with a neurologist to see which treatment option is most suitable. 

However, telling the difference between single and multiple seizures isn’t always as straightforward as it sounds. For example, if someone has multiple seizures over a few hours (without complete recovery between them) this can still count as a single seizure.  

If someone is having a prolonged seizure (where the person is unresponsive for five minutes or more) it’s likely that doctors would want to administer emergency treatments – usually an injection – to stop the seizure from continuing.

This treatment is important, as seizures can affect someone’s breathing as well as their heartbeat.  

Sometimes people with prolonged seizures may need to be admitted to intensive care to keep them physically stable while they recover.

Why might a person with dementia not be prescribed anti-seizure medication?

If a person living with dementia has a single seizure, doctors may decide not to prescribe an anti-seizure medicine – even though having dementia means the person has a higher risk of having further seizures.

There can be several reasons for this. Some doctors may be concerned that starting an anti-seizure medicine could interfere with other important medicines that the person is already taking.

Others may be concerned that an anti-seizure medicine could cause side effects or make dementia symptoms worse.  

Sometimes, however, starting an anti-seizure medicine may actually help a person’s dementia – at least over the long-term. This is because people who have more seizures in dementia tend to have a faster rate of cognitive decline, so preventing further seizures with medicines may stop this accelerated decline.

Newer anti-seizure medicines are also less likely to interfere with other medications or cause side effects.

This article was first published in 2019 and most recently updated in September 2022.