Neuro Podcases: An approach to... localisation (part 1)

Transcript

[Music] Welcome to another episode of Neuro Podcases, a clinical neuroscience podcast.

[Music] So hello, my name is Arina and I'm a neurology trainee working at the Walton Center.

Thank you for listening to this episode of our Neuro Podcases.

Today we'll be talking about localization, which is actually a topic that is often dreaded, but very, very important for all medical students.

So today's podcast will be sort of pitched at the medical student level, but neurology trainees might also find it helpful.

And today I am joined by Dr. John Williamson, who normally actually interviews for our for our series, but today he will be the person giving his expertise.

Hello.

Hi, Arina.

Thanks very much.

And yeah, it's nice to be on the receiving end of the questions today.

So let's start with the sort of basic question, just thinking what do we actually mean when we say localization and why do we care about it so much in neurology?

Okay, so yeah, good place to start.

So when we think about localization, it's important to put it into context of when we're seeing a patient who has a neurological problem, our first thought is obviously whether the symptoms the patient has relate to, you know, disruption of the nervous system.

And then we have to think whether or not this is something that has caused disruption to how the nervous system is structured versus how the nervous system is functioning.

And then if if we think the person symptoms could relate to structural damage to the nervous system, the next question we've got is where in the nervous system the problem might be.

And there's obviously, well, that can be quite a lot of answers to that question.

But generally we think could this be a focal neurological problem.

So a problem with just one part of the nervous system, or could it be a problem that's multifocal spread across many parts, or could it be a diffuse problem affecting the whole of the nervous system or a whole region of the nervous system.

That's what what it is it's working out where in the nervous system the problem is.

And it usually comes as a combination of both the history and the examination.

And I guess today's podcast we'll be talking about how the examination can really help you localize.

That's absolutely correct.

I guess sort of, you know, I would agree with you, but I do have a little bit of a question to challenge because I guess in the sort of, you know, previous day and time we could say that's really important because you know exactly where the problem is.

But surely these days we can scan people.

And that sort of would help us very much and narrow our differential, isn't it?

Yeah, well, I'll take that as a deliberately provocative question.

It is.

Yes.

Okay.

So, yeah, I think obviously, you know, in we obviously do a lot of scanning and, you know, I guess MRI would be a very common investigation, whether it's the brain, the spinal cord.

And to take the question very seriously there, we have to think, well, how do you know which part of the nervous system to scan?

And, you know, you don't just do whole body MRI on someone just because they have a problem of the nervous system.

And, you know, sometimes we deal with conditions where perhaps the scan doesn't give us the answer.

So, you know, it's all very well thinking we'll scan the brain.

But if you've actually localized the problem to being in the nerves or the muscles, then obviously a brain scan isn't going to give you the answer.

So, it's about working out which bit to scan and also really thinking whether a scan is appropriate.

And there's actually another way to think of it as well, which is that very often patients will get scans done for other reasons.

And the question will be, well, could this be explaining the symptoms?

And I think working backwards, you have to be able to work out how to localize to work out whether or not a scan finding could be relevant.

So, lots of reasons to learn it.

So, it actually hugely affects the practice, doesn't it?

Yeah, I think it's something that all neurologists would be, would say is quite an essential part of the job.

Yeah.

Well, so I think my duty is to say I've been persuaded as a neurology trainee.

So, then let's start with the localization.

And perhaps the first question I could ask you is sort of what is the basic anatomy that one needs to keep in mind in deciding sort of where the delusion is?

Okay.

So, yeah, it's difficult to know where to start, I guess, but probably a sensible place to start is with the motor system.

So, if a patient has weakness, now, you'll have taken a full history and from the history, you can work out the potential options of where that could be.

But if we just go a brief recap of our neuroanatomy, we can start to think a bit more systematically about that.

Okay.

So, if we think of our motor pathways, so it's very simple in terms of the upper motor and lower motor neuron pathway that we have to think about.

So, let's start with the upper motor neuron pathway, which starts in the cortex, where the cell body resides.

And we've got to remember that the motor system is arranged in a very particular way in the cortex.

And I'm sure we all remember the pictures of the homunculus, where you have the face and the hand very close together and then the arm and then the legs are the more medial part of the cortex.

So, you've got the homunculus there, which is the cortical representation of the motor system.

And then, that motor neuron will go on a journey through the subcortical white matter and that will take it through to the brainstem, which is another important landmark.

And at the brainstem, something very important happens, which is the motor fibers cross over.

So, that happens in the lower part of the brainstem called the medulla.

And then, from the medulla, it becomes the spinal cord.

And in the spinal cord, the motor pathways travel in the lateral corticospinal tracts.

And that's a single neuron.

So, that's all the way from the cortex to the lateral corticospinal tracts is a single neuron.

And then, that neuron will eventually terminate or synapse in the anterior horn, the ventral horn of the spinal cord.

Okay?

That's one long journey, isn't it, for one cell.

So, that's all.

Absolutely.

That's one neuron.

And if you damage that neuron anywhere along that pathway, it will give you similar clinical signs.

So, the way that you help to localize where on that pathway it might be damaged is by looking at the other accompanying signs that come with it.

But we'll get to that in just a moment.

So, it synapses in on the anterior horn cell and then it forms, then it becomes the lower motor neuron.

So, this is the second neuron in that pathway.

And the lower motor neuron then exits the spinal cord via the ventral root, nerve root, and becomes a mixed motor and sensory nerve.

So, it becomes a mixed motor and sensory nerve root.

The nerve roots will combine to become, in the upper limbs will become the brachial plexus.

And then, the brachial plexus will divide out and become individual nerves.

And then, it's not quite over yet.

So, when it gets to the nerve, it then will terminate as a nerve, but you have the neuromuscular junction and then you have the muscle.

And, or anywhere disruption on any of this pathway, the upper motor neuron, the lower motor neuron, the neuromuscular junction, or the muscle could potentially present with weakness.

Okay.

So, that's the sort of whole motor nervous system in a nutshell, isn't it?

Yes.

Yeah.

And I think what's really important to remember is that patients might present with symptoms that are, that are weakness or similar to weakness that are due to problems of how this motor system is controlled.

So, these can be extra pyramidal problems.

I guess the most typical one would be Parkinson's disease.

But you can have problems of too little movement like Parkinson's or too much movement like a career.

But the, I guess the fundamental unit of movement is this upper motor neuron, lower motor neuron connection.

Yeah.

And then, obviously, it's also under influence from other things such as the cerebellum, which could present with weakness or something that looks like weakness.

And even, you know, other more higher cortical functions that could cause an apraxia.

But for the purposes of localization today, we'll just focus on this upper motor neuron, lower motor neuron pathway.

Perfect.

So, I guess the first question is there, and if there is a weakness in our patient, is it then a lower motor neuron or upper motor neuron, a sort of type of weakness?

So, the question is sort of what type of examination findings you would expect?

And whether it is actually easy to tell in practice whether it is upper or lower motor neuron?

Yeah, so, very good question.

So, let's deal with the damage to the upper motor neuron first.

So, when patients have damage to the upper motor neuron, the muscles that are affected will have a very characteristic clinical findings.

So, we tend to see increase in tone, which is a very specific sort of increase in tone, which we call spasticity.

Okay?

The reflexes, when you test the reflexes in upper motor neuron damage, reflexes tend to be brisk.

And in particular, there's one reflex that's very important called the babinski response or the plantar response.

And that tends to be up going or extensor when there's been damage to the upper motor neurons.

And then, if you damage the upper motor neurons, there tends to be a very distinct pattern of weakness as well.

So, you may hear people talk about a pyramidal pattern of weakness.

So, this is a very distinct pattern that's different in the upper and lower limbs.

So, in the upper limbs, a pyramidal pattern of weakness means that the flexors are strong but the extensors are weak.

And in the lower limbs, it means the opposite, it means that the extensors are strong but the flexors are weak.

And if you see a patient that has that combination of signs of brisk reflexes, strong flexion in the upper limbs with extension in the upper limbs and strong extension in the lower limbs with weak flexion and an up-going plantar, well, then you've pretty much got all of the signs there to suggest that this is a person who's got an upper motor neuron problem.

And then, your only question then to ask is where in the pathway the problem might be.

So, I'm sort of thinking in my head about stroke patients with sort of this very typical pattern of a sort of, you know, curled up arm, isn't it?

Exactly, yeah.

And as we know, stroke is a disease that affects the central nervous system.

And therefore, it's no surprise that the examination findings that you get there are upper motor neuron findings.

If you've damaged your lower motor neurons, you tend to get, so you get absent reflexes, you have flaccid tone and you would expect the weakness to not follow that pyramidal pattern.

You wouldn't expect the plantar response to be up going.

But you asked whether it's always easy to make that distinction in clinical practice and the honest answer is, you know, I wish it was always that easy.

But, you know, these things can be a bit tricky and, you know, patients don't tend to read the textbooks before they come in.

So, I think what you have to do is have a very meticulous approach to examination, examine lots of patients and hopefully you pick up the signs.

But you can be caught out.

I think the classic thing that we're always taught and we always teach students is someone presenting with a fairly acute spinal cord syndrome.

They could present with, say, flaccid weakness in the lower limbs as a very acute, during the very acute stage.

So, it does take time for those upper motor neuron signs to evolve and develop.

Absolutely.

I remember sort of finding it quite tricky to understand how sort of, for example, stroke patients can look as if they had a lot of lower motor neural lesion, whereas in fact, the lesion is in the brain.

I think, yeah, that's really important.

And we did discuss in another podcast, actually, with my colleague, Dr.

Regan Cooley, about how to assess a stroke patient.

And I think stroke is one of those examples where it's all very acute and it's all very quick, especially because if you want to give treatment and you're not looking for these signs, you're not looking for brisk reflexes, pyramidal pattern weakness in a stroke patient, because it's happening then and there in front of you, you're not going to find them.

So, in that situation, you're just looking, is there weakness and trying to localize based on the pattern of weakness that you're seeing?

Of course.

For today, I think we'll stick to the basics though, hasn't it?

So, I think that's quite a good framework to start with.

So, you have the sort of upper motor neuron signs, which would be spastic weakness and increase reflexes with outgoing planters, and that will bring you sort of straight onto the central nervous system.

And then, sort of, you know, for lower motor neuron, you would have this flaccid weakness with absent or reduced reflexes.

So, we sort of roughly know where we are.

But how do we go farther from there and sort of what are the patterns of weakness you might see with the damage to upper motor neuron at various levels?

So, for example, the brain hemispheres, the brainstem, or the spinal cord.

Okay.

Yeah, so I think this is where it's really important to look for patterns of weakness.

And obviously, you're going to, as part of your examination, you're trying to think is this upper motor neuron versus lower motor neuron.

But the distribution of where the weakness is can also be a really big clue.

So, let's start in the brain.

So, we know because of how we're wired that the right hemisphere, that those motor fibers are destined to innovate the left side of the body.

That's just how things work, right?

So, if you have a problem that's affecting one side of the body, be it leg, face, or arm, that's your first clue that this may be a hemispheric problem, rather than maybe a spinal cord problem.

And then, within the cerebral hemisphere itself, we've got the various levels there.

So, in the cortex, if you have a problem affecting the motor neuron near the cortex, you might expect to see other cortical signs there.

So, let's take a condition like stroke.

So, if you've caused weakness by damaging the upper motor neuron at the level of the cortex, then what you would also expect to see is perhaps if that weakness is down the right side of the body, you would expect to see maybe problems with language because we know the left hemisphere, the areas that control our motor control of our face and our arm are very close to Broca's area, which is obviously important for the output of language.

So, that can be a clue to helping localize to not only the cerebral hemisphere, but particularly a cortical problem within the cerebral hemisphere.

If you go down a bit further from the cortex, the fibers are running in the subcortical area, which is the white matter tract.

Now, if you damaged the upper motor neuron in the, I don't know, the left hemisphere subcortical white matter, you would expect the weakness to be down the right side of the body again because we're in the hemisphere, but you wouldn't expect there to be those other cortical signs.

Okay?

That makes sense.

So, you have the sort of unwanted bonuses with the cortical signs, the extra sort of deficits.

Yeah, and certainly, I guess the stroke syndrome that we know most likely is a pure motor lacuna stroke syndrome, where you can have weakness affecting the face, arm and the leg down the one side of the body, but you don't get problems with speech.

You don't have problems of a hemianopia, and that's because the damage is being done at a site distant from where those other cortical areas are.

The important thing to think about with the subcortical areas as well are in the homunculus, these neurons are spread over a lot, quite a large surface area, but as they travel through the brain, they all come together to be very close.

So, you can have a very small lesion or very small area of damage in say the internal capsule, and that could give you very severe weakness down the whole side of the body, and that's also important to remember as well.

Yeah, very special areas in that internal capsule, absolutely.

Then we get to the brainstem.

So, in the brainstem, the motor fibers, so through the midbrain and the pons, the motor fibers will be traveling down, and they will be on the same side as they were in the hemisphere.

So, damage to those structures again will give you the opposite side weakness, but the important thing about the brainstem is that there's lots of cranial nerve nuclei there as well, and the cranial nerve nuclei, they're exiting at the level of the brainstem.

So, if when you're examining someone, you can see that they've got weakness down maybe one arm and leg, but they've got cranial nerve signs on the opposite side to the weakness, then that's a really strong localizing sign that the problem might be in the brainstem.

Absolutely.

Have you heard of the rule of four of the brainstem?

I think I did, yes.

So, four at the top, four in the middle, four at the bottom, roughly, isn't it?

So, that's kind of a good way to think about where in the brainstem you might have the problem.

So, if you've said four at the top, so if you've got a third nerve palsy affecting the left eye, and you've got weakness in the arm or leg on the right side, then you can say, well, that's the left side of the midbrain.

Absolutely, yes, because cranial nerves will always be sort of affected on the same side, whereas for the rest of the body, we are talking about the decussating pathways, isn't it?

And then, not quite finished yet with this upper motor neuron, so you've still got a little bit to do, which is the spinal cord.

Of course.

So, we're saying we've crossed over at the bottom of the medulla, and we're traveling in the lateral corticospinal tracts.

Now, the upper motor neuron will then travel down until the level at which it's synapses in the anterior horn cell, as we've said.

One of the clues often to a spinal cord pathology, though, is that they can often be quite symmetrical, and this is because the cross-sectional area of the spinal cord is actually quite tiny compared to the brainstem and the brain.

And so, any disease process, be it a stroke, inflammation, a tumour, is likely to affect, to some degree, it might be asymmetric, but it's likely to affect both sides of the spinal cord.

So, if you see someone who's got weakness, both arms, both legs, you have to think to yourself, could that be a spinal cord problem?

It's not over at that point.

You've still got a bit of work to do, but that's just the starting point.

Of course.

So, sort of putting it all together, if I am in this sort of hemisphere in the cerebral cortex, I would expect sort of other cortical signs, then going a little bit deeper, it would be probably more of a sort of pure motor sort of symptoms and signs.

Brainstem would give me the cranial nerve signs and symptoms, and then if I am in the spinal cord, then weakness is more likely to be bilateral, although it might be asymmetrical.

Is that sort of where we are for the upper motor neuroneum?

As a general rule, that's really good.

And then, I guess the important thing is to never be, you know, to keep an open mind and always be trying to think logically about it, but it's a really good starting point.

Of course, sure.

So, sort of then thinking of the sensory examination, because most patients, of course, will present with both motor and sensory findings.

How does that help us to sort of ascertain where we are?

And I guess we'll probably need to revisit the pathways as well, isn't it?

Yeah.

So, so far we've only talked about the motor pathways, but you're right that there are these sensory pathways as well.

And that can help us with the task of localizing.

So, we usually do the sensory exam towards the end of the motor exam.

So, you've already got a bit of a hypothesis as to what you think the problem might be.

And I guess the way I would tend to use the sensory exam is you have to then test that hypothesis with the sensory exam to think, like, is there sensory involvement at all?

Because sometimes we can help localize by there not being sensory involvement.

And if there is sensory involvement, what's the pattern of that involvement?

So, let's do a brief recap.

So, now the nerves are traveling in the opposite direction.

So, they're traveling from the periphery into the spinal cord and then up into the brain.

Okay, so, let's start with the out in the out in the periphery.

So, we obviously have our sensory nerve endings and these then travel in often mixed motor and sensory nerves.

They travel through the brachial plexus and then they'll enter the spinal cord at the through the dorsal roots.

Then this is where it then gets slightly interesting because there's two roots then from going into the spinal cord up into the brain.

And I think the students kind of know this, but if it's worth recapping it and having a picture as you think of this.

So, you've got what we call, let's deal with the dorsal columns first.

So, these are the sensory fibers that convey vibration and joint position sense.

When they enter the spinal cord, they will, they don't synapse immediately, but they will travel up the same side of the spinal cord as to what they've entered until they get to the very top of the spinal cord just on the junction with the medulla where they will then synapse.

And then once they are in the, once they synapse, they then go into a bundle of nerve fibers which is called the medial lemskis and the medial lemskis goes to the thalamus, but it crosses over to the opposite thalamus.

So, if it's been in the right dorsal column, those fibers will go into the left thalamus.

And then from the thalamus there are then projections up to the cortex.

So, it's a three-order neuron pathway.

Correct.

Okay.

The spinothalamic tract is a bit different.

So, the spinothalamic tract will enter through the dorsal nerve root and it will synapse in the dorsal horn of the spinal cord, gray matter.

It will then cross over at that level.

So, at that level or a few levels above to the opposite side and it will travel up in the anterior lateral or the spinothalamic tracts all the way to the thalamus.

Okay.

So, that's the pathways.

So, how does the sensory exam help inform our localization?

Well, if you've got a problem that's affecting your spinal cord, you would be looking to see how do you, is it also affecting the joint position, vibration and pain or temperature sensation?

If it's affecting all of them, then you would think to yourself, well, that's likely to be an entire cord problem, like a transverse myelitis.

If it's affecting some or not other, that would help you localize which side of the cord it's on.

In the brainstem, so it's, the whether or not pain and temperature can help you to decide, does this localize to the medial aspects of the brainstem, where the medial lemoscus travels?

Or is it in the more lateral aspects of the brainstem where the spinothalamic tract travels?

So, that can be a helpful localization along with the motor system findings and the cranial nerve findings.

And then at the level of the cortex, obviously, if you have a very large stroke that's affecting the motor cortex, well, we know the sensory cortex is just behind that.

So, you might there see a similar pattern of motor and sensory, you might see a similar pattern of sensory symptoms to where you have the weakness Okay, so confusing, but hopefully.

No, I think I'm still following.

Yes, definitely.

So, just sort of moving then from the central nervous system to the peripheral nervous system.

We talked about the sort of motor and signs that one would expect, so signs of lower motor and neural lesion.

And then again, thinking of the sort of sensory examination findings and how they would come into play.

And you mentioned already a sort of, you know, sometimes the absence or presence of sensory signs is a helpful localizing sign as well, isn't it?

Yeah, so when we we're talking about the lower motor neuron, now, so we're talking all the way here from the anterior horn cell through the ventral, sorry, through the ventral root out of the spinal cord and into a mixed motor sensory, into a mixed motor sensory nerve root.

So, nerves from different nerve roots will combine to form either the brachial plexus or the lumbar sacral plexus to the lower limbs.

And from there will emerge individual nerve.

And then we talk about the neuromuscular junction and then the muscle.

So then we've damaged the lower motor neuron.

We know what characteristic findings we would expect.

So how do we localize it a bit further down than just just saying just like is a periphery.

So I think what's really important to think about the concept of what a myotomis is.

So a lot of people know what a dermatomis, a dermatomis, an area of skin supplied by a certain sensory, by a sensory nerve root.

And so a myotome is similar, but with muscles.

So take for instance, the T1 nerve root, there will be motor nerve fibers within the T1 nerve root that are destined to become, that are destined to innovate the first dorsal enterosius muscle, so muscles that would control finger abduction.

And some of them will also even go on to innovate abductor policies brevis, so the muscle of the thumb.

So if you damaged at the level of the T1 nerve root, you might have weakness of both first dorsal enterosius and also abductor policies brevis, right?

But actually, each of those two muscles are actually innovated by a different nerve.

So the first dorsal enterosius is the ulnar nerve, and the abductor policies brevis is the median nerve.

So you've got this discrepancy there that if you've got both of them affected, well, it's either both an ulnar and a median neuropathy, or it could be a problem higher up at the level of the nerve root.

And that's kind of how you work out localization of the lower motor neuron.

You have to look at what muscles are affected, and then think back and think like, so what nerve does that?

What branch of the brachial plexus is that?

So which part of the brachial plexus does that come from?

Which nerve root does that come from?

And it's kind of like, you know, sorting it out.

It's like, well, if it's this and this, then it has to be this.

It's kind of a logical deduction from there.

It's a lot of pattern recognition, isn't it?

And sort of experience.

And I guess probably many students might find it scary to sort of memorize exactly, you know, which nerve root, which nerve.

What are your tips for sort of committing such things to memory?

So I think the, I think that what I would say is that when you examine, obviously when you learn the neurological examination, it, you'll start learning it just as a process of, right, you need to get through it and learn how to pick stuff up.

But I think it's really important when you are testing, every time you test a muscle, just to think to yourself, okay, what nerve is this that I'm testing?

And that's one way to start.

The other is that there's lots of really good textbooks, and one that a lot of neurology trainees will use is called AIDS to examination of the peripheral nervous system.

It's a really good textbook.

It's in there.

And I think that's a really good, good resource for students to use.

And then the sensory exam, I guess it works in a similar way.

So it kind of augments what you found on the on the motor exam.

So with that, if you've got problems with the nerve roots, as I said before, those are mixed motor and sensory nerves.

So you would expect to see dermatomal patterns of sensory loss.

That's, and I think everyone knows on YouTube, there's a dance that you can do to learn the dermatome.

I've never learned that.

Yeah, yeah.

It's out there.

Something to go to.

And so you'd expect dermatomal symptoms.

And probably in the history, you'd expect there to be maybe pain as well, because irritating a nerve root or damage to the nerve root would cause a lot of symptoms.

And then likewise, if you if you have a mixed motor and sensory nerve affected, so the ulnar nerve, then you would expect there to be sensory loss in the distribution of the ulnar nerve.

So this sensory exam can be useful.

And then if there's no sensory involvement, well, then you might start to think about more things that could this be a problem with the anterior horn cell.

So that lower motor neuron before it joins with the the before it mixes with the sensory nerves to form a mixed nerve root.

Absolutely.

And apart from that, we'll also have certain muscle and neuromuscular junction diseases.

Oh, yeah.

And that also leave us with no sensory symptoms or signs.

Yeah, really, really important.

So if you if it's a muscle problem, you're not going to have sensory sensory signs.

And if it's neuromuscular junction, you're not going to have sensory signs and signs.

And usually, you know, those sorts of things as well, most muscle problems, not not all, but most muscle problems, you'd expect to be quite symmetrical.

Usually they affect proximal more than distal, although there are some quite important exceptions to that.

And neuromuscular junction disorders will usually the hallmark of those is fatigue ability.

That means that as you exercise as you exercise the muscle, it tends to get weaker.

There are some that can get stronger as you exercise, but that kind of that the fact that exercise changes the strength.

That's a good localizing sign.

Sure.

Yes, absolutely.

Okey-dokey.

So I think that sort of covers the very basics of sort of localization, isn't it?

Just sort of pulling it all together.

We are starting with the motor nervous system and looking at the sort of upper and lower motor pattern of the lesion.

Once we roughly know if we are central or peripheral, then we can sort of use the extra features.

So for example, looking at the cranial nerves, thinking if the damage is symmetrical for the spinal cord, thinking whether we are just affected on one side of the body, as we would do with sort of most cerebral hemisphere lesions.

And after that we can, as you say, verify our hypothesis with sensory examination and say, is this fitting?

And potentially use a couple of textbooks for those sort of nitty gritty details of nerve roots and nerves.

And obviously, all of what we've said so far occurs in the context of also having done a thorough neurological history as well.

Unless it's a medical examination, it's very rare that you would just walk up to someone and start examining them.

So you get most of your information about the hypothesis of what might be wrong from the history.

And then the examination kind of fits in after that to try and narrow it down further.

So it's a sort of multi-level approach really, absolutely.

Great.

So I think there are just a couple of special situations and maybe confusing scenarios that certainly I found slightly more confusing as a sort of medical student.

Because we've built our system sort of based on those upper and lower motor neuron findings, would you be able to tell me if there are any situations where I might find both of them actually?

Yeah, okay.

So probably a bit of a leading question because there are obviously situations where you can get both.

So obviously, first thing to say is patients might have two pathologies.

So that's always a possibility.

So someone may have had a stroke who also happens to have, I don't know, diabetes and they've got a peripheral neuropathy with the diabetes, giving them reduced ankle jerk response and they've had a stroke, which means they've got some spasticity also on that side.

So that's, but then I guess a couple of things to really think about with what you're saying is if you say you had a spinal cord problem at the level of, I don't know, the C5-6 of the spinal cord.

So let's say, for instance, there's a disc that which is very common pathology there that's pressing or irritating the nerve root as it leaves the leaves the spinal cord.

So at the level of where you've got, sorry, so let's say there's a disc that is both impinging on the spinal cord itself, causing a myelopathy.

So impressing down on the spinal cord, damaging the upper motor neuron pathways that are traveling down the spinal cord in the corticospinal tracts.

But the same disc is also causing pressure on the exiting nerve root at that level.

So C5-6.

So what you might see here is that the level of C5-6, which as we know is the level that controls muscles such as our biceps muscle and is would be expected to be is important in the biceps reflex arc.

You might see lower motor neuron signs because you're damaging the lower motor neuron there.

But below that level, because we've got the pressure on the spinal cord, you would see upper motor neuron signs below the level.

And we know that the triceps reflex, for instance, is at the level of C7-8.

So in that scenario, you might have a brisk triceps reflex, but a reduced biceps reflex.

And that might seem a little bit confusing.

But I guess that's actually that would be a very good way of thinking this is actually localizing to the spinal cord.

And you can even be a bit more specific.

There are very few places that would give you a sort of this pattern of reflexes.

And I think reflexes are really useful to know about your reflex levels in general, because it can help localize within the spinal cord.

You know, spinal cords are long as a long structure.

And there's a lot of areas it could be damaged in.

Obviously, it should be obvious that if the problem affecting the spinal cord is occurring in the thoracic spine, you would not expect any motor problems in the arms, because all of the arms, certainly below the level of T1, all of the nerves that are destined to become motor nerves to the arms will have left.

So if you have a situation where there's weakness in both legs, but there's no weakness in the arms and reflexes and examination of normal in the upper limbs, that would tell you that this probably is a, you know, this is probably in the thoracic spine or lower.

And likewise, if the problem is affecting both arms and legs, and you've got upper motor neuron signs in the arms and legs, and, you know, in particular, I guess if you've got a sensory loss, that's the other, yeah, sorry, a sensory level, that's the other thing, then this would tell you that that is a cervical problem.

It wouldn't make sense for that to be a thoracic level problem.

Absolutely.

And is there another sort of condition that you could think of giving upper and motor neuron signs that I think would be worth to mention here?

Yeah, so the other condition, of course, is motor neuron disease.

And this is a neurodegenerative disorder affecting both the upper motor neuron and the lower motor neurons.

And depending on how, you know, which is affected and where it's affected, you can get a combination of both upper and lower motor neuron signs.

And I guess the classic thing that you might see there is a muscle that is weak and wasted, which is a very lower motor neuron sign.

But there is also a brisk reflex present there.

And that kind of tells you that there may be a condition like motor neuron disease there.

Importantly, the sensory exam there, you'd expect to be completely normal, because that's only a condition that would affect motor nerves.

Absolutely.

Great.

So I think that's sort of one of the tricky situations that I wanted to discuss.

And then I think the other one that is perhaps most hated by medical students and so-called the Brown-Essai-Cord syndrome, which is the sort of spinal-hemicord lesion, would you be just sort of able to pull together all we've discussed and say, you know, what sort of signs and symptoms would you get?

And I think that would be probably a good way of summarizing all that we covered so far.

Yeah, good.

So we kind of alluded to this earlier, but let's deal with it now.

So if you have a problem affecting just one half of your spinal cord, thinking about what you'd expect to see on examination is a good way to think about those pathways in general.

So obviously, let's take for instance, where you have damaged the right side of our spinal cord.

So we'll say this has been damaged at the level of the cervical spine for simplicity.

So what would you expect to find from a motor pathway?

Well, we know that the upper motor neurons that run in that part of the spinal cord have already crossed over.

So we would expect the weakness to be down the same side as the pathology.

So we'd expect right-sided arm and leg weakness.

Agreed?

Agreed.

And I can also add that would be an upper motor neuron sort of.

And it would be an upper motor neuron weakness.

Yeah, absolutely.

And then what would we expect for the sensory exam?

So this is where it's really important to remember where the spinal thalamic and where the dorsal columns cross over.

So the dorsal columns, if you remember, they travel up on the same side as they enter until they get to the very top of the cervical spine at the base of the medulla and then before they sign up and cross over.

So if you damage the right side of the spinal cord, you would expect the loss of vibration sense and joint position sense to also be on the right side.

So the same as the upper motor neuron findings.

And I guess the opposite is then true for the spinal thalamic tracts.

So we would expect because these have entered and have crossed very early after entering, that actually the spinal thalamic tracts running up the cord will be conveying sensation from the opposite side of the body.

And that kind of dissociated sensory loss is very localizing to the, to a right hemic cord syndrome.

I think the important thing to state is that doesn't tell you what the cause of the person's problem is, you know, that's where you need to do a history and maybe do a junctive test, but that would localize very strongly to the spinal cord.

Absolutely.

Have you ever seen that in practice and what was the etiology just of curiosity, because it's quite a rare syndrome as an example?

In practice, what you tend to see is patients who have kind of like a partial Brown-Sequard.

So there might be some elements of it where there is this dissociation of joint position sense and and pinprick.

So and the conditions tend to be with that would be more the neuroinflammatory such as MS, like an MS plaque on just one side of the cord could do that.

Sure.

So I think we've covered sort of the basics.

We've discussed the sort of more complex scenario.

We've discussed where we would see the sort of combined upper motor neuron and lower motor neuron signs.

Discuss the sort of sensory patterns for the peripheral nerve examination and also for the central nervous system examination.

And we also touched upon the brainstem.

And we talked about sort of localization using them, cranial and nerves nuclei.

Is there anything else you would like to add on or any sort of tips for our students?

Yeah, I hope that I hope we've not lost too many at this stage.

And I think the key is that everything we've talked about here is not in isolation.

So this is all comes from taking a history, forming a hypothesis about what you think might be wrong, and then using the examination as a means to test that hypothesis.

I hope that what patients, what you know, what students listening would now appreciate is that there's a large element to this, which is pattern recognition.

But even if it's not pattern recognition, having a systematic approach to it and thinking quite logically can get you quite far.

And what I really would hope is that actually they've seen that this is one of the reasons why neurology is an interesting subject and why it combines that, what's really important about being a doctor, which is taking history, examining and really working at the bedside and using the bedside as your laboratory to try and work out what's going on.

And I guess being logical and sort of systematic, methodological is what we like to think of ourselves as neurologists, I guess, is it?

Yeah, that's how we like, yeah.

And localization is what we sort of consider to be the great example of that.

Yeah.

And, you know, and sometimes, obviously, I said it at the start, and I think it's worth stressing is, you know, sometimes after the history, your hypothesis will be that I don't think this patient has a structural problem with the nervous system.

I don't think they've, and therefore you would use the examination to test that you would expect it to be normal.

And, you know, you don't, it's not that every neurological examination you do, you will be finding pathology, it's just when you do find pathology, trying to work out where in the nervous system it is, that's the important thing.

So, brilliant.

Thank you very much.

I think that completes me grilling you on the other side of the microphone.

Thank you for listening.

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