Sensory Examination

00:01 Alright, so now having assessed the strength and the reflexes, it's time for us to move on to examining the sensory part of our nervous system.

00:10 Patients who have either an acute spinal cord problem like from trauma or transverse myelitis or something like that, versus somebody who has a radiculopathy or a peripheral neuropathy entrapment, its useful for us to get a sense as to what the patterns are of sensory loss that can occur and how to assess the different components of the sensory exam, that's going to be important as well.

00:31 So first off we're going to talk about light touch.

00:34 So light touch is actually best assessed with the use of the so-called Semmes monofilament.

00:42 I've got one right here, so the Semmes-Weinstein monofilament is designed to apply a specific amount of pounds per square inch such that once you've applied that pressure, it buckles and that allows us to be very specific no matter who's doing this test, no matter where in the world they're using it, you're getting the exact same amount of sensation applied to the skin.

01:03 So now we're going to go ahead and use our Semmes-Weinstein monofilament.

01:07 In general, what we'll do is I'm going to have Shaun close his eyes, please, and then we're going to actually touch on five different parts of his - the ball of his foot, two spots on the ball of his foot and then three different toes.

01:20 Let's see how he does.

01:22 Lift up your foot for me please, great, and I just I want you to say yes every time I make contact.

01:28 Yes.

01:30 Yes.

01:32 Yes.

01:35 Yes.

01:36 Yes.

01:38 Perfect. You'll note that I tried not to be perfectly regular there because you want to catch your patient's from starting to predictably say yes, if I'm going out in exact frequency.

01:48 Patients strangely will sometimes cheat on this test if you give them an opportunity to do so, so it's good to be sneaky in that regard.

01:56 So as I've mentioned before, this is an extremely useful tool that can predict an ulcer down the road in folks with diabetic polyneuropathy has a very strong likelihood ratio of developing an ulcer within the next two to four years, if any of those five points were not detected on physical exam.

02:12 Next stop, lets assess vibrations sense. So let me get my tuning fork.

02:17 Typically when we're assessing vibration sense we use this 120 hertz tuning fork.

02:25 Alright, so first off we're going to make sure we're using the right language and that's important in communicating with patients.

02:31 So I'm going to ask you to put your hand out for me, please.

02:32 Face palm down, yeah, and this is a vibration, do you feel that? Mm-hmm Or is this just touch, good? Yeah.

02:41 Alright. So now we're going to go down and do the same thing on his feet.

02:45 I'm going to start distally and if I work to detect abnormal vibration sense, I would simply move proximally from one joint to another until I found the point where vibrations sense was present and in this case I'm going to use the on-off approach and you'll see what I mean once we do it.

03:04 We go down here, apply this to his great toe, do you feel that vibration? Yes.

03:11 Great, I'm going to ask you to keep your foot up there.

03:13 Now just tell me when the vibration goes away. Stop.

03:18 Perfect, so that tells me that he has intact vibration sense distally and I simply kept it running and then as soon as I stop it, he perceived it to be stop, that's intact vibration sense.

03:29 Sometimes people will just let it linger there until vibrations goes away, but it's very difficult to know what exactly should be normal when you're trying to find the right threshold of time that has elapsed since you last hit it because everybody's going to hit it a little bit differently, your on-off approach is a little bit more precise way to do that.

03:46 If he were not to have a sensation on the big toe, I would have moved to the first metacarpal, of the metatarsal joint, then I would have moved proximal along to one of the foot bones potentially the navicular bone and then ultimately to the medial malleolus and you just keep on marching until you find a place where things are normal again.

04:03 Now, next stop is proprioception which is the ability of you to know where your joints are, where your limbs are in space even with your eyes closed.

04:12 And it relies upon intact spinal cerebellar tracts running up your spine.

04:18 So in general, a person should be able to detect as little as one to two degrees of movement in a joint with their eyes closed.

04:25 So I'm just going to assess his hands first, so if you could just put your hands out in front of me.

04:29 Actually, just one hand is fine and I just, I'm going to hold the sides of his middle finger here.

04:36 I just want you to tell me if you feel your finger moving up or down, okay. Up, down.

04:46 That was it that was two degrees of motion at the most.

04:49 So in general our ability to discern, to what extent our joints are moving around in spaces is pretty good.

04:55 Now, folks who have diabetic polyneuropathy with this glove and stocking distribution of sensory loss which involves the longest axons in the body first.

05:04 They will oftentimes lose vibrations sense and proprioception first and then they may lose light touch sensation with the monofilament.

05:13 Which is why it's so important to make sure with the monofilament, we do catch things early and so that's a part of our routine diabetic foot exam every year.

05:20 So we'll do assessment of proprioception in his feet as well.

05:25 So similarly, I'm grabbing the side of the toes rather than the top and I just want you to tell me while I'm splinting his other toes out of the way, whether you feel your toe going up or down. Up. Up.

05:42 Great. Tried to trick him there by going up twice.

05:45 Importantly I'm not grabbing the finger or the toe from top to bottom because the pressure that I would be applying on top or bottom of the finger would be a clue to as why whether not I was moving the toe up or down.

05:57 So that's it for proprioception, vibration sense and light touch.

06:02 There are other senses that we do sometimes assess at the bed side for example you can test temperature by getting some ice or getting some heat.

06:10 Sometimes even something as simple as using the coldness of my tuning fork compared with my finger and asking the patient to tell the difference between those two temperatures, but often times it's - often times assessing temperature doesn't have a lot of diagnostic utility except in very specific situations with particular neurologic diseases and then pin prick, which is assessing for pain sensation, can also be useful but in general if it comes to screening, we mostly just use the three approaches that I've already demonstrated.

06:43 It's also useful to have some sense of the distribution of dermatomes in the body so we'll just cover that very quickly.

06:50 I talked before about the muscles and the reflexes that are involved in different nerve roots.

06:56 I also always have to anchor myself by remembering that C6 is your thumb and your first finger and for me I think back to old western movies from the 1950s which involves cowboys using their revolvers which had six bullets, they were called six shooters and so this is how, if I was a kid, playing cowboy and robbers, cops and robbers, I would be using my six shooter, so this is my C6 dermatome.

07:25 And now that I know that this is my C6 dermatome, I know that proximal to that must be C5 and distal to it is going to be C7 which is your middle finger, C8, T1 rounding here at the bottom of the forearm back towards your axilla which is going to be T2.

07:40 Your nipple line is T4 and heading down to your umbilicus is T10, so those are the, basically we've just marched all the way from C5 all the way down to T10 and then the lower extremities, you can always remember that around the anus is S2 to S4 and then marching backwards here there's some discrepancy but exactly where does S5 end up but usually it's wrapping around the toes here.

08:06 So folks who have sciatic nerve dysfunction or sciatica, will often times have pain that goes all the way down the leg out to the outside of the toes and those are the main dermatomes that we really need to keep track of when we're talking about assessing for nerve root dysfunction and sensory radiculopathy.