Hi, I'm Dr Michael Vagg and in this short video I'm going to be demonstrating some of
the sensory findings that can help with the diagnosis of neuropathic pain.
The patient who we're going to be examining today is called Matthew.
He's a 45 year old man in good general health who's developed some burning pain down in
the left leg into the foot and some back pain as well and that's been there for a few weeks
now and seems to be getting a bit worse.
The possible diagnosis of radicular pain is what we're going to test by doing some sensory
examination.
Okay so Matt's on the bed here and we're going to be examining his lower limbs from a sensory
point of view.
It's always important to remember to test one dermatome against another and one side
against the other.
So I'm going to focus on the L4, L5 and S1 dermatomes on each side, which is represented
by the medial part of the calf, the dorsum of the foot and the lateral part of the ankle
respectively.
We’re going to begin with Light Touch.
I like to use the tip of the brush to test light touch, although, if you don’t have
a brush, something like a tissue which can be rolled up is fine.
So Matt, can you feel that?
[Matt] Yes
Can you feel me touch you there?
[Matt] Yep
And there?
[Matt] Yep
What about on here?
[Matt] Yeah
And there?
[Matt] Yep
And there?
[Matt] That’s a bit less there
Okay, so that’s a bit less?
[Matt] Yeah
And then
[Matt] That’s more
There compared to there
[Matt] The same
Okay
So it looks as if there may be loss of light touch sensation consistent with an L5 dermatome
change.
So I’m going to move on now to testing pinprick sensation.
I like to use a toothpick for this because many patients who may have neuropathic pain
will be very sensitive if they have hyperalgesia so you don’t want to use anything too sharp
because some of these patients may have a very heightened sensitivity to pain.
I find that using a toothpick creates a sensation of sharpness with very little risk of causing
significant harm or distress to the patient.
It’s very important to make sure your testing is consistent, to hold the toothpick so that
it slips through your fingers each time that you touch the skin and then that means you’re
using a consistent amount of pressure each time.
So we’ll go again through our dermatomes with the toothpick.
Matt, can you tell me, do you feel a sensation of sharpness?
[Matt] Yes
And there?
[Matt] Yes
And here?
[Matt] Yep
And here?
[Matt] A bit less there
That’s a bit reduced?
[Matt] Yeah.
And here?
[Matt] Yep.
That’s normal?
[Matt] That’s normal, yeah.
[Matt] Yeah, that’s normal too
Okay.
So again we have a reduction to pinprick sensation consistent with the L5 dermatome on the left.
The last modality I’m going to test for is one of the most important ones when you’re
trying to make a diagnosis of neuropathic pain.
If it’s present, it’s a very sensitive sign that there is again a function change
in the nerve and it’s highly correlated with the presence of neuropathic pain.
To test we use for this is to run the brush dynamically across the skin.
So rather than just using the end of the brush, one strokes the skin, just with enough force
to bend the bristles of the brush.
This is referred to as a test for dynamic mechanical allodynia.
So, through the dermatomes again.
Okay Matt, can you feel me
[Matt] Yeah
touching you there?
Does that feel normal?
[Matt] That feels normal, yeah
And on that side?
[Matt] That’s normal
On this side?
[Matt] Normal
That’s L5
[Matt] Yeah
And there?
[Matt] Yeah
[Matt] Oo-yuh!
Okay, so that, can you describe that sensation as I brush there?
[Matt] It’s pain there
So that’s painful?
[Matt] Painful
And right there to the end?
[Matt] Yeah
And then on the outer part?
[Matt] Oh, that’s okay
That’s okay, that feels normal on both sides?
That’s the same on both sides?
[Matt] Yeah
Okay, so we’ve demonstrated in Matt the findings of reduced sensation to light touch,
or hypaesthesia to light touch, as well as reduced sensation to pinprick.
And increased sensation to dynamic stimulation with the brush, otherwise known as brush allodynia.
These findings support the diagnosis of nerve dysfunction in the L5 dermatome because they’re
anatomically consistent and will then provide you with support for your decision as to whether
or not this is neuropathic pain.