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Neuropathic pain: Physical examination sensory tests

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.

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