E - Dermatomes

Question 1

What is the definition of a dermatome

Answer 1

A strip of skin innervated by a single spinal nerve

Question 2

Why are dermatomes of clinical diagnostic importance?

Answer 2

They allow clinicians to determine damage to the spinal chord and if present, the extent of that damage

Question 3

Where do dermatomes originate?

Answer 3

The third week of embryogenesis - tri laminar disc

Question 4

Which structure do dermatomes originate?

Answer 4

The paraxial mesoderm

Question 5

Where is the paraxial mesoderm?

Answer 5

The portion of the mesoderm directly adjacent to the neural tube

Question 6

From day 20, what does the paraxial mesoderm develop into?

Answer 6

44 different segments called somites. 13 of these break down, leaving 31.

Question 7

Each of the 31 somites develops into…

Answer 7

1 spinal nerve

Question 8

Each of the somites have…

Answer 8

Ventral (front facing) and dorsal (back facing) segments

Question 9

Ventral portion of somites

Answer 9

Sclerotome - precursor to ribs and vertebral column

Question 10

Dorsal portion of somites

Answer 10

Dermomyotome - myotome proliferates and the dermatome disperses to form the dermis of the skin

Question 11

As precursor of the limbs grow (skin)…

Answer 11

The dermis associated stretches with their development, and forms the Keegan and Garrett dermatome map of 1948

Question 12

The two clinically accepted dermatome maps

Answer 12

Keegan and Garret map of 1948, Foerster Map of 1933

Question 13

What does the 1948 dermatome map depict?

Answer 13

Dermatomes in a way which correlates with segmental progression of limb development

Question 14

What does the 1933 dermatome map depict?

Answer 14

The upper limb being innervated by T1-T3 (spinal nerves) and follows their distribution of pain from angina or a myocardic infarction

Question 15

Most commonly used dermatome map

Answer 15

1933 Forester Map - used in the ASIA scale to assess spinal injury

Question 16

What do both dermatome maps depict?

Answer 16

Limb progression around an axial line, with there being only a small overlap between adjacent dermatomes

Question 17

Dermatomes can be used to diagnose the presence of…

Answer 17

A spinal chord lesion after a traumatic injury

Question 18

First step of spinal chord injury assessment

Answer 18

Cotton wool with light touch along limbs and torso to test for light touch sensation along different dermatomes

Question 19

Second step of spinal chord injury assessment

Answer 19

Responsiveness to pain - patient is asked to close eyes and asked to say when they feel a pin make contact with their skin

Question 20

Why are light touch and pain assessed differently in spinal chord injury assessment?

Answer 20

Their nerve fibres travel in different parts of the spinal chord.

Question 21

Why is spinal chord assessment taken out?

Answer 21

To note any regions of paresthesia, to ascertain whether there is nerve involvement, and to determine whether it is at a spinal root or peripheral level.