Hello all this is Dr Alsup and in this video we will be discussing cutaneous maps.
And everyone loves a good map and in this video we will be discussing how to differentiate between
a dermatome and a peripheral cutaneous nerve map and when I say the word cutaneous what does that
make you think of? Hopefully you recall it means relating to or affecting the skin so these maps
tell what nerves will innervate particularly or particular parts of the skin.
And we're going to start with the dermatome map and we actually touched on dermatome maps
all the way back in our first session but that was a long time now so let's review
here. A dermatome map shows the areas of skin innervated by a single cranial nerve or spinal
nerve and it's really the spinal nerves that have the bigger expanse. And the dermatome map is going
to be on the left side here with the peripheral cutaneous map on this other side and you can see
that for the upper limb say specifically it's mostly cervical spinal nerves that are
going to serve these particular areas with a little contribution from t1 or thoracic spinal
nerve one. And when looking at the upper limb you can see some distinct patterns and understanding
the development of the limbs is very helpful for understanding why it looks like this.
Now the limbs grow as lateral protrusions from the trunk with the first digit or the thumb located
on the cranial side or the superior side. So obviously this isn't developmental in this image
but this is an adult here but you can think of development as in this direction.
Therefore the lateral side of the upper limb will have more cranially directed spinal nerves as
you see here so the higher cervical numbers and the more medial surfaces are innervated by more
inferior spinal nerves so c8, t1 that's why it's going to be be directed in this position.
A dermatome map is different from a peripheral cutaneous map so again
this is the dermatome side this is peripheral cutaneous and this will depict areas of skin
innervated by specific peripheral nerves and so typically nerves that are branches of plexuses
and these will be multi-segmental meaning it has fibers from more than one spinal nerve. So
again this is the peripheral cutaneous map on this side and you can see named nerves throughout here.
So why would there be different maps? Well if a patient is experiencing numbness or tingling
in a particular area, if you think it is nerve damage like pinching or something worse it could
indicate damage to a specific cranial or spinal nerve so a more proximal lesion or damage or
and but more importantly or damage to a peripheral cutaneous nerve so a more distal lesion. So from
your knowledge of a reference to both these maps this can help guide you to best understand what
specific nerves need to be tested, so both at the spinal nerve level as well as at the
cutaneous peripheral nerve level to get at the root of the issue so it's more proximal issue
is it a more distal issue and you can kind of go from there with your knowledge of these maps.
Excellent we have reached the summary slide. Now of likely interest to you
while you can certainly use these maps for reference, you do not need to memorize as in
it won't be assessed the specifics in this map unless it comes up in another learning objective.
Instead please focus on understanding the difference between the types of maps, so
what a dermatome map is going to tell you and what a cutaneous peripheral map will tell you.
As always please reach out with any questions and thank you for your time and attention