8 julio, 2024

Dermatome: what it is, types and clinical significance

A dermatome It is an area of ​​the skin that is innervated by a single spinal nerve. Specifically, they are controlled by sensory neurons that arise from a spinal nerve ganglion.

There are eight cervical, twelve thoracic, five lumbar, and five sacral nerves. Each of these nerves allows us to feel temperature, touch, pressure, and even pain.

The information travels from a specific region of the skin to the brain. The dermatomes are arranged as a stack of discs on the thoracic and abdominal sides, each disc being supplied by a separate spinal nerve.

In the extremities the pattern is different. In this way, the dermatomes traverse lengthwise the arms and legs. Thus, each half of each limb has a different dermatome.

Although all individuals tend to have the same general pattern in the organization of the dermatomes, the specific areas of innervation may vary in each person, much like fingerprints.

The spinal column has more than 30 different vertebrae that are divided according to their location, starting with the neck up to the coccyx. They are classified as cervical, thoracic, lumbar, and sacral. Each vertebra contains a specific spinal nerve that will innervate specific areas of the skin.

All nerves except the first cervical nerve (C1) are connected with a dermatome. Dermatomes make it possible to build a very useful map of the spinal cord for health professionals and researchers. As well as for the diagnosis and treatment of pathologies.

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What is a dermatome?

Have you ever wondered why back pain gives rise to tingling sensations in your legs? Or why neck cramps make your fingers feel numb?

This appears to be because there is a link between the sensations and irregularities on the skin’s surface with the particular nerve roots leading from the spinal column. Therefore, each region that is innervated by each of these nerve roots is called a dermatome.

Dermatome is divided into “dermat”, which means “skin”, and “oma” which means “mass”. We have 29 dermatomes in the human body. These nerves are related to each other, since they originated from the same somite groups during embryonic development. Somites are structures formed on the sides of the neural tube during the fourth week of human development.

For example, nerve fibers from the surface of the skin that covers part of the legs and feet form a dermatome that comes from a nerve root in the lower back.

types of dermatomes

The dermatomes, like the spine, are differentiated into four sections: cervical, thoracic, lumbar, and sacral. Each dermatome is classified according to the spinal nerve that innervates it. That is, the seventh cervical nerve would innervate the C7 dermatome.

That dermatome would give sensitivity to the skin of the shoulder, parts of the arm, and the index and ring fingers.

cervical dermatomes

They innervate the skin of the nape, neck, back, arms, and hands.

Thoracic dermatomes

These cover the skin on the inside of the arm, chest, abdomen, and mid-back.

Lumbar dermatomes

They innervate the skin on the lower back, the front of the legs, the outer thighs, and the tops and bottoms of the feet.

sacral dermatomes

These cover the skin of the genital and anal areas, the back of the legs, the back of the thighs and calves, as well as the outer edge of the feet.

However, it is important to mention that dermatomes have been discovered in recent years by clinical observations and are only a guide. Each person may present slight variations in the limits of the dermatomes.

Dermatome maps

To better visualize the distribution of dermatomes, there are mainly two maps accepted by anatomical medicine. The first is the 1948 Keegan and Garrett map. While the second is the 1933 Foerster map. The latter is the most widely used.

The two maps show the growth progression of the limbs around an axial line. Although the dermatomes do not appear superimposed in the image, it is true that there is a slight overlap in some parts of the route.

clinical significance

It is important to know how dermatomes work in the clinical setting to locate nerve or spinal cord lesions.

If certain symptoms are located along the area associated with a dermatome (pain, skin irritation, rashes…) it may be due to something related to the nerve root. For example, a herniated disc that compresses the L5 nerve root results in pain and tingling in the lower leg and foot.

Dermatomes are useful for establishing a diagnosis and treatment of different conditions. The main ones are viral diseases, radiculopathy and spinal cord injuries.

Viral diseases

There are certain viral diseases that are located in specific dermatomes, such as herpes zoster. This virus is latent in the spinal cord and when manifested it moves through the spinal nerve causing a painful rash on the skin that is associated with that nerve.

The shingles rash is usually limited to a specific dermatome such as on the chest, leg, or arm. It usually appears years and even decades after recovery from chickenpox.

radiculopathy

This condition consists of pain caused by damage to the root of any nerve. It can also cause a loss or reduction of sensory function. The most common affected regions are L5 and S1, and less commonly C6 and C7.

The pain increases when we put ourselves in positions where the nerve roots are stretched. It can be cervical or lumbar depending on where the pain is.

spinal cord injuries

When there are spinal cord injuries, the healthcare professional will look for the affected dermatome. To do this, he will start with the part of the skin where the patient has noticed changes. He will go around it with a pin or a fork on both sides of the body until normal sensation is reached.

You can also check if it picks up vibration along the vertebrae. Usually, the sensory level is two or three levels below the lesion.

Difference with myotomes

Dermatomes should not be confused with myotomes. While the dermatomes are involved in the sensitive part of the skin, the myotomes are responsible for the innervation of the skeletal muscles of the same somite group.

For example, in the lower part of the trunk they are responsible for flexing the thigh, extending the knee or extending the big toe.

References

DERMATOMES. (nd). Retrieved on April 16, 2017, from Teach me anatomy: teachmeanatomy.info.
Dermatome Map – Overview Chart, Anatomy, & Clinical Significance. (nd). Retrieved on April 16, 2017, from Pain care: paincare.org.
Dermatomes. (nd). Retrieved on April 16, 2017, from Queen’s University at Kingston: meds.queensu.ca.
Dermatomes. (nd). Retrieved on April 16, 2017, from Boundless: boundless.com.
Kishner, S. (nd). Dermatomes Anatomy. Retrieved August 12, 2015, from MedScape: emedicine.medscape.com.
What is a Dermatome? –Definition & Distribution. (nd). Retrieved on April 16, 2017, from Study: study.com.

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