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Course: Health and medicine > Unit 8
Lesson 11: Multiple sclerosisMultiple sclerosis diagnosis
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Want to join the conversation?
- I have read that a patient who gets a spinal tap cannot be sedated. Why is this so?(4 votes)
- Hi, Kevin. There is some historical bias against sedating patients for lumbar puncture, but many patients are, in fact, given something for the procedure. There are two traditional arguments against sedation. One, the sedative could potentially cloud a practitioner's ability to assess an evolving neurological process (i.e. what the LP was ordered for). Shorter-acting sedatives have made this argument less relevant. Two, sedation might render an already possibly-confused patient prone to sudden movement during the procedure, which could potentially lead to injury. Because LP's are typically done in the low lumbar spine (i.e. lower than the position of the spinal cord), this risk is more theoretical than actual.
In any sedation or anesthetic, it is ideal to match the medication administered to the patient's presentation, medical history, and procedure to provide optimal operating conditions for the provider doing the procedure, while placing the patient at the least possible risk of harm. Like many things in medicine, it is a matter of degrees, rather than absolutes. Though some dogmatists state that sedation is not permissible during lumbar puncture, it is simply not the case. Hope this helps.(4 votes)
Video transcript
- [Voiceover] Let's say you're a clinician and you want to tell if
someone has multiple sclerosis. One of the first things you might do is you might actually
look into their brain. The way to do this is to use a technique called Magnetic Resonance Imaging, otherwise known as MRI. What you do is you have
someone lay down on this bed and they enter this kind
of cramped and really loud machine over here. That machine is actually gonna
take pictures of their brain. Interestingly enough, it's
actually gonna take pictures from three different perspectives. On the left, we kinda
have a picture of someone who looks like they're
looking towards the left. This slice of the brain is
called a sagittal slice. In the middle, it looks
like we have a slice of someone who's looking
in this direction. So it's kinda as if we're looking down from the top of their head. We call this a horizontal slice. On the far right, we
have a slice of someone who looks as though they're
looking towards or away from me. We call this a coronal slice. In all three slices you'll
see one thing that's common. They have this bright spots over here. These bright spots that
they actually point out. These bright spots are
referred to as lesions. A lesion is just a
piece of damaged tissue. If you think someone
has multiple sclerosis and you have all these brain scans, the first thing you're gonna look for are these bright spots here. These bright spots are actually located wherever there is a white matter. Remember that the white
matter is really just the axons and the myelin of your neurons. So this informative, right? You see that you have damage in the brain, but that damage could
result from anything. So we haven't really
narrowed down specifically. We can still do a few more tests to really confirm that
this is multiple sclerosis. We can actually do something that is a little bit more invasive. Here I have a picture
of someone's lower back. In purple here is the
person's spinal cord. You can see this kind of blue stuff that's surrounding the spinal cord and that stuff is just called
your cerebrospinal fluid. The cerebrospinal fluid just bathes both the spine and your brain. It contains all sorts of good things; proteins and ions and all
sorts of things that you need for the brain and spinal cord to work. What we can do is we can actually extract that cerebrospinal
fluid using this needle, and we can collect it into this vial. Now we have a vial and that vial has a whole
bunch of cerebrospinal fluid, but the question is, what is
in that cerebrospinal fluid? There's going to be something in here that's characteristic
of multiple sclerosis. What is that thing? Remember that multiple sclerosis
is an autoimmune disease so the immune system is
really crossing paths with the nervous system. We want to see something
that's characteristic of the immune system. So maybe if we kinda zoom in here. What's characteristic
of the immune system? Well, antibodies. If you have a lot of antibodies
in your cerebrospinal fluid then that may indicate
that your immune system is in the central nervous system. How do we determine if there
are antibodies in here? We can use a technique known as gel electrophoresis. I'll spare you the details of how exactly this technique works. But really what it does is first it separates the
contents in your sample and it allows us to
visualize those contents. Basically, we're gonna
send this vial off to a lab and they're going to
perform gel electrophoresis. When you separate the contents of this cerebrospinal fluid and
when you visualize it, it looks something like this. Here, I kinda have two
different strips for you. The left strip corresponds
to a person who is healthy. The right strip corresponds
to someone who has multiple sclerosis. Immediately, you'll notice
that there are these white bands over here. These bands, they're gonna
correspond to different proteins. In the healthy sample, you'll
notice that these bands are separated uniformly. But in the multiple sclerosis sample, you'll see that there are
these thicker bands over here. These thicker bands are referred to as oligoclonal bands. When you see these oligoclonal bands, that's actually pretty
indicative that there are a lot of antibodies in this sample. Because you have a lot of
antibodies in this sample, that means you have a lot of antibodies in your cerebrospinal fluid. That tells us that the immune
system is really really active in the central nervous system. So we have two pieces of evidence. We have pictures of the
brain that showed the lesion and we have evidence that shows that the immune system is involved in the central nervous system. But there's still one
more test that we can do to definitively say that this
person has multiple sclerosis. We can actually measure
the electrical activity in the person's brain. Let's say you have a person here and he's just sitting in a dark room, and you put these electrodes
here onto their scalp. Those electrodes are gonna
measure their brain activity. More specifically, it's gonna
measure the brain's response to some kind of visual stimulus. In this case, it's a computer screen. On your computer screen,
you have a checker board. You have all these black tiles and you have all these white tiles. These tiles are actually
going to alternate every half second or so. So maybe every half second
so, all the black tiles are now in pure white,
and all the white tiles will now be pure black. It's just gonna alternate back and forth. We're basically measuring
the brain's response to this visual stimulus. That response is gonna be called a visual evoked potential. What are we measuring here? Well, we're measuring
an electrical response. We're gonna measure it graphically. Let's say we have a graph over here. On the x-axis is time, usually
on the scale of milliseconds. And on the y-axis, we have voltage, usually on the scale of microvolts. Let's say we're kinda measuring
the person's brain activity and at some point the
checker board alternates, and we're gonna see this
kind of peak in the voltage. It's gonna go back down
and continue onwards. We're gonna be looking at these peaks in response to the
alternating checker board. Usually, you collect
data from a lot of peaks, but this is just one such example. Now, given that this is a
visual evoked potential, you're gonna be measuring activity from visual areas in the brain. Let's say you have your eyes over here, so this is the person's eyes. At the back of the eyes
are the optic nerves. The optic nerves will
carry visual information in the form of electrical
activity to the rest of the brain. Let's just say for the sake of argument that this person has a lesion
in their left optic nerve. The right optic nerve,
however, is perfectly healthy. So when we measure the electrical activity from both of the optic nerves,
we can actually compare them. We can compare activity
from the healthy optic nerve to activity from the damaged optic nerve. Let's say that the graph
that I've drawn here, as it is now, is just the
optic nerve that's healthy, so it's the right optic nerve. Then you look at the electrical activity from the left optic nerve, it might look like something like this. Immediately, you could
tell that there's actually a delay between the two. It took a longer period of
time for the left optic nerve to respond to the
alternating checker board. This actually makes a lot of sense because if we think back to it, let's say we have a neuron over here, ordinarily your neurons
have a bunch of myelin that insulate their axons and this myelin helps
the electrical signals travel then a lot more
quickly on the axon. But in multiple sclerosis,
that myelin gets degraded. When that myelin is degraded, the signal that moves down
the axon is a lot slower, so when you have all these degraded myelin over here on the left optic nerve, it makes a lot of sense for the signal to be slightly delayed. I wanna make it clear that these signals that I've drawn here aren't
actually action potentials. They're signals that you
get from the overall nerve. But in general, the
principle is still the same. You see there's a delay in the response. So the left optic nerve is now slower than the right optic nerve because you have this lesion over here. So all in all, I've shown
you three very common tests that people use when
diagnosing multiple sclerosis.