Now, if I do this and the person feels pain, we call this allodynia, and allodynia is an
abnormal sensation, of course, because this is just a light touch, very light, so should not
hurt. but some people will feel pain. Hi, I'm Dr Andrea Furlan, and today I'll be talking about
sensory examination. how this is important, how it is done in a patient that has chronic pain.
So, let's talk a little bit about sensation, one of the sensations we test in people with chronic
pain is sensation to light touch. so light touch we use a paper tissue like this, or a cotton ball,
and if we touch the skin of a person that doesn't have any abnormality in the sensations, they will
feel this, like a light touch. now if I do this and the person feels pain, we call this allodynia,
and allodynia is an abnormal sensation, of course, because this is just a light touch, very light. so
should not hurt. but some people will feel pain, and uh some people also, when I do this they will
feel numbness, they will be anesthetized. they will not feel it, so that's also abnormal. So,
what's going on? this is called allodynia. Allodynia means it's a painful sensation, the
person the brain receives information that this is dangerous, this is painful, but it's not. we know
this doesn't hurt. this is not damaging my skin, so what is the problem? why the brain perceives
this as dangerous? we actually don't know where is the problem, but we know that there is a problem,
and this problem can be a transduction in the receptors of the skin, so the problem can be here,
where the receptors are, but we know that these receptors they travel, there is an electrical
impulse that will travel to the spinal cord, they use fibers that are kind of large fibers, they are
A-Beta fibers, they have myeline, they're kind of large, so they go pretty fast, they arrive in the
spinal cord, so it could be in this, when they're traveling to the spinal cord, in the nerves, that
there's some crisscross or there's a short circuit there, or it could be in the spinal cord itself,
it could be at the level of the spinal cord, that there is when the impulse enters the spinal cord
in the dorsal horn, thatthere's something there, or it could be from the spinal cord when it's
going up to the brain, so this crisscross, this short circuit can happen in many places, what we
know is that there is something abnormal, that's why we call allodynia. it's interesting that
allodynia is also possible we can have allodynia to pressure, so if I apply certain pressure to
my skin, should not hurt, but if I apply a lot of pressure then it's going to hurt, right? so
what is a little bit of pressure, what is a lot of pressure? it's usually by the time that my
nail starts blenching, then I know I'm applying too much pressure, so if I'm just touching and
apply a little bit of pressure, and the person feels pain, that's also called allodynia. it is
pressure-evolved allodynia. this is touch-evoked allodynia, we can also have allodynia to hot
things, if I apply something hot to my skin that a normal person without abnormall would feel this is
warm, or this is hot, but it's not painful, if I apply to someone who has allodynia to warm because
those are different fibers, those are C fibers, that carry that information, then I detected
allodynia to a warm-evoked allodynia. I can also evoke allodynia with cold, if I apply something
cold to the skin, and a normal person would say oh this is just cold, but it's not hurting, and I if
I apply this to a person that has abnormality in the pain system, they're going to say no, no, no,
this is hurting me, so anything that is above we call hyper, anything that is below we call hypo,
so a person can have hyper sensitivity, or hyposensitivity. The other sensation that we also
test is the pain fibers so those those are the A-Delta fibers, and we usually use something that
is sharp, like could be a toothpick ,a needle, a sharpie thing, could be a paper clip that we open,
so something that is very sharp, because now, this thing here is activating different fibers,
different from this ones these are certain receptors detect this sensation in the skin,
this is a different one and they go from different fibers, this go A Delta fibers, this go through
the A-Beta fibers. A beta is larger than the A Delta, and the warm sensation goes to the C-
fibers, C fibers they don't have any myeline, so they're very, very thin, we call those the
small fibers, so if I'm testing something that is painful, so this is not pleasant, so this is kind
of activating the pain receptors and my brain is detecting this is pain, but it's pain that I can't
tolerate, now if I do this in a person that has an normal pain system and the person I do this and
they jump, they say what are you doing? it's Too Much! I Feel Like a Knife! this is not a knife,
this is just a toothpick, but they feel like a knife, this is called hyperalgesia. they're
feeling more the pain. Algesia means pain, hyper is more, so more pain to a stimulus that is small,
the person may also have hypoalgesia, that this is supposed to hurt it's not pleasant,
we call and especially if I start doing a lot the person should say it's not pleasant, but if the
person say, no I don't feel, I feel blunt, like uh it looks like you doing something like this,
it's not like this, that's abnormal, that's hypoalgesia. now if I do this and the person
has no idea where I'm touching, I usually do this test with the person with the eyes closed,
I ask them to close their eyes, and then I test, and sometimes I'm touching their skin, and they
have no idea where I'm touching, because they are numb, they are anesthetized, so then we called
it's not even hypoalgesia. It is anesthesia, they have no sensation, now why this is so important?
because these are all the sensors that we have for danger, and our skin is so innervated with sensors
for danger, we have tons or millions of sensors around our skin, and we have sensors for light
touch, for pressure, for heat, for cold, for pain, because we do need to alert our brain of what is
going on outside of our body, so our pain, or our skin is our interaction with the exterior ,so it
is important, because then we can detect there are some abnormal Sensations, abnormal your pain
system is deregulated, so why is deregulated? so the question is what makes this pain system
deregulated? and I can explain to you there are a lot of things that can deregulate the pain system,
the sensations, they are it's important that we map them, so usually I start with this area
here of the face of the patient. because this is innervated by the trigeminal nerve, it's usually
preserved, this area, it can be abnormal, but it's usually preserved, and then we compare
the rest of their body with the face, so I do this ,and I say compare your face with your arm,
is it the same? is it more is it less? and I ask them to close their eyes when they're doing this,
and then it's important that when I do this for all Sensations, we do this for all of those,
and then what we do is we also want to try to map is this the hemibody that is abnormal? that could
be a stroke, it could be a thalamic problem, is it just one arm? then it could be a radiculopathy,
so if there is a very specific portion of my arm that is like here I know this is probably C6,
so the cervical six nerve root, on this side that might be being pinched, because I have
abnormal Sensations on my C6 dermatome, or it could be that it's just in this area here,
that is innervated by the median nerve. the median nerve is a nerve that innervates this part here,
is usually affected when a person has carpal tunnel syndrome, so if everything else is normal
but the area of the median nerve is affected, I okay, maybe all of these abnormal Sensations
are happening because there is a median nerve compression here, at the wrist, and this is called
carpal tunnel syndrome, it's a neuropathic pain, and then there a neuropathic symptom,
now sometimes these abnormalities they don't follow a pattern, it's not a nerve root, it's
not a brain injury, it's not a spinal cord injury, it's not a peripheral nerve, and they change, the
important thing is like a in the morning, this was hyper and now in the afternoon it might be hypo,
we see this all the time, and um this is because it's nociplastic pain, so plasticity in the pain
system changes, and it can change the day, the time of the day, it can also change with the how
the the emotions of the person, are if the person is more stressed, more fearful, more angry, they
may have more hyperalgesia, more Sensations, if they're calm, and they can calm down their system,
especially the sympathetic nerve system, some of those abnormalities can normalize, because that's
nociplastic pain, so that's why it's so important for us to do a physical examination, including the
Sensations, because we can detect allodynia. we can detect hyperalgesia, hypoalgesia,
and we can also do another test, that we can do, we can also do a test called the hyperpathia,
so what is hyperpathia, we use the sharp, we use the painful stimulation, and we do we choose one
area that the person has pain, usually the area of most painful area, let's say that the person says
oh here, is my the most painful area, it's here, so we'll do here, we'll do one sensation, we'll
do one this, is It's it has to be the painful one, and then we keep repeating like once every second,
so we keep repeating this, so if a person has the normal pain system, especially in the spinal cord,
they don't have the wind up phenomenon, they will feel all of these Sensations will be felt the
same, so we ask them to give a number, I say from 0 to 10 how unpleasant is this? so they can say,
oh it's a two out of 10, I say okay so I keep repeating this maybe one per second,
or two per second, and then if the person has hyperpathia, which is a sign of neuropathic or
nociplastic pain, then they will be adding this pain, so it's almost like each one of them adds
more pain, so at some point ,they will say it's getting worse, it's getting worse, stop, because
then you reach a threshold that is too painful, if you detect thi,s it's called hyperpathia,
and then it's a sign that they have the wind up phenomenon in the spinal cord, and we see
this with nociplastic pain, and also some case of neuropathic pain, so that's why it's so important
to do this the sensory exam, doctors should learn how to do this, and should do this when they're
examining a patient with chronic pain, especially if they have any signs of neurological pain, or
nociplastic pain, because those signs are really important for a complete physical examination.