STN-DBS versus GPI-DBS – Which DBS location is better?

Worldwide, the most common DBS location is a brain part called the Subthalamic Nucleus (STN-DBS). So, most doctors think it is better.

But in some patients, an alternative location may be better. This alternative location is the Globus Pallidus Interna (GPi). In fact, some doctors think that GPi-DBS is better in all cases!

Your doctor will do this thinking for you. He/She will tell you the proposed location.

But, its good to know how he/she thinks!

Let us learn quickly about the pros & cons of these locations.

What do you mean by DBS-Location?

DBS passes a small electrical current into a small brain part.

The small brain part is called the DBS location. Many doctors will call it the DBS Target instead.

Look at the picture below.

See the wire going into the brain? The location where it ends is the location that will get the current. That is the “DBS location” (or “DBS Target”)

You could use any location in the brain. But doctors have found two great locations already.

The names of these two locations are:

• Subthalamic Nucleus (STN)
• Globus Pallidus Interna (GPi)

Subthalamic Nucleus (STN-DBS)

Where is the Subthalamic Nucleus (STN)?

The STN is deep, very deep, inside the brain.

There is one two STNs. One on the left, and one on the right.

They are also tiny. Like peas.

Ok, so close your eyes, and imagine. Two peas, almost touching each other, in the centre of your head, just below your ears.

That’s it! That is where the two STNs are.

What is the benefit of STN-DBS?

Let us say your doctor puts the end of the wire into the STN. And switches on the small current. What happens?

STN-DBS decreases the symptoms of Parkinson’s disease.

• You need less levodopa after STN-DBS. Usually, the levodopa dose can be gradually reduced by 1/2.
• STN-DBS also keeps acting throughout the day, so it decreases “Predictable-OFFs”.

A simple example:

Let us talk about an imaginary person – Mr. Salisbury.

Mr. Salisbury is already taking 12 tablets of levodopa. He takes 3 tablets every 4 hours.

A few minutes after he takes this high dose, he gets nauseous and sometimes starts shaking too much. But he insists “But I absolutely need this dose to function!”

“I know these are Dyskinesias” he says. “But I put up with them because I need that high dose of levodopa to function!“.

That is not all. Just 2 hours after taking the levodopa, it’s effect wears off. Mr. Salisbury goes into the OFF-state again. He almost completely freezes. This wearing-Off is very predictable.

After STN-DBS, Mr. Salisbury becomes ON with only 1.5 tablets of Levodopa. Not only that, the effect now lasts for 4 hours.

Even when he goes into the OFF-state, he is not completely OFF. He does not completely freeze.

Mr. Salisbury is particularly happy that his levodopa dose has decreased. Because his dose has decreased, he has less severe dyskinesias.

In summary:

STN-DBS decreases both Predictable-OFF & Dyskinesias.

But, the effect on dyskinesias is indirect.

What are the side-effects of STN-DBS?

STN-DBS causes two characteristic side-effects.

• Increasing severe depression, if you already have it.
• Increasing memory problems, if you already have them.

STN-DBS may rarely cause depression or memory problems. But this is rare. Mostly, all it does is to increase severe problems, if you already have them.

So, if you already have these very severe problems, STN-DBS may not be the right choice.

What can you choose instead of the usual STN-DBS?

If you have these problems, and they are severe, you should probably not choose usual DBS.

You can choose:

• Not to have DBS or
• STN-DBS of only one side or
• DBS of another target called the Globus Pallidus Interna (GPi)

If depression or memory problems are extremely dramatic, then not having DBS may be considered.

For borderline problems, many doctors consider another target – the GPi. This is called GPi-DBS.

Globus Pallidus Interna (GPi-DBS)

Where is the Globus Pallidus Interna (GPi)?

The GPi is not as deeply located as the STN.

There are two GPis. One on the left, and one on the right.

The GPis are bigger. They are shaped like this yo-yo here.

Imagine a small yo-yo like this, inside your head, just above your ears.

That’s it! That’s where the two GPi are.

What is the benefit of GPi-DBS?

Overall, GPi-DBS causes the same benefits as STN-DBS. But, the way it does so is different.

GPi-DBS decreases the side-effects of levodopa, especially DYSKINESIA.

Let’s consider an imaginary person, Ms. Mary.

Ms. Mary is not able to take enough levodopa to decrease his symptoms. She can only take 4 tablets in a day.

Why? Because when she takes more tablets, the body starts shaking too much. Like the video below, posted by a brave patient on youtube. These movements are called “Dyskinesia”.

“I really wish I could take more medication!” says Mary. “But if I try to increase it, this dyskinesia just becomes intolerable!”

Wouldn’t it be wonderful if these bad movements went away? GPi-DBS does that.

After GPi-DBS, Ms. Mary can take 8 tablets per day without any side-effects. Her Parkinson’s symptoms are much better.

After levodopa is increased, will GPi-DBS benefit Mary as much as STN-DBS would have?

Yes. The latest research indicates that the improvement in movements is similar.

In summary:

GPi-DBS decreases Dyskinesias. It enables you to take enough levodopa. The net improvement is similar to STN-DBS.

So, both lead to the same amount of improvement… what is the fuss about?

Well, you see, GPi-DBS may have fewer side-effects.

The Sub-thalamic nucleus (STN) is part of a system that controls emotions and memory. This system is called the limbic system. So, both emotions & memory suffer when DBS overloads the STN.

The GPi isn’t intimately connected to emotions or memory. Therefore, DBS of the GPi has a lesser chance of producing these side-effects.

Does GPi-DBS have any disadvantages?

Not many.

Some doctors believe that GPi-DBS is ever so slightly less effective. But, other studies show no difference. Overall, its safe to say that there is no dramatic difference in improvement between STN-DBS & GPi-DBS.

The GPi is slightly larger than the STN. So, it requires a somewhat higher current. This can make the DBS battery run out sooner.

Let us quickly summarize. GPi-DBS:

• Produces almost the same improvement in movement as STN-DBS
• Decreases Dyskinesias
• Is less likely to worsen depression
• Is less likely to worsen memory problems.
• May need more frequent battery replacement.

STN-DBS versus GPi-DBS

When is GPi-DBS better than STN-DBS?

The answer to this question will seem very simple now.

Should GPi-DBS be done in all cases, instead of STN-DBS?

Ah! My friend… so some people have raised the next question.

If GPi DBS is equally effective and has fewer side-effects, why not do it in all cases?

Some authorities have indeed suggested that it should replace STN-DBS as the DBS location of choice.

The answer lies in two words: Customized Care.

1. Suppose you have a patient who is taking 12 tablets of levodopa daily. He still has marked Predictable-OFF and moderate dyskinesia. What would be a good target? STN
2. Suppose you have a patient, who is mildly depressed. She is taking only 3 tablets per day but still has severe dyskinesias. What would be a good target? GPi
3. Suppose you have a patient who really, really wants to decrease his levodopa intake, because it is causing severe uncontrollable nausea. What is a good target? STN

And so on…

There are many Antibiotics, because there is a time and place for each one.

There are two DBS targets, because there is a time and place for each one.

Each one of us is unique. We need treatments selected for our uniqueness.

Further reading / References:

Here are some resources if you want to read further. They may be too technical though.

1. Here is a good scientific article on this topic, if you want to read it: [Ramirez-Zamora et al 2018 – JAMA Neurology]. You may need University Access to get the full text.
2. Here is a freely accessible article. It describes the thought process as it relates to a single patient. [Patel et al 2017 – Tremor & other hyperkinetic movements]

I know that this information can be overwhelming.

As for all these articles on DBS, I would like to end my article with the picture below. Have a long talk with your doctor. He/She will help you make the right choice.