DERMATOME: WHAT IS IT, TYPES AND CLINICAL SIGNIFICANCE - ANATOMY AND PHYSIOLOGY

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

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.

Foerster Map

Information travels from a specific region of the skin to the brain. Dermatomes are organized as a stack of discs in the thorax and abdomen, each disc being supplied by a separate spinal nerve.

In the extremities the pattern is different. In this way, the dermatomes run longitudinally through 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 dermatomes, the specific areas of innervation can vary from person to person, much like fingerprints.

The spinal column has more than 30 different vertebrae that are divided according to their location, starting with the neck 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 to a dermatome. Dermatomes allow the construction of a map of the spinal cord that is very useful for health professionals and researchers. As well as for the diagnosis and treatment of pathologies.

What is a dermatome?

Anterior view with the dermatomes and main cutaneous nerves. Source: Mikael Häggström. Public Domain File

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

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

Dermatoma 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 on the surface of the skin that cover part of the legs and feet, make up a dermatome that comes from a nerve root in the lower back.

Posterior view with the dermatomes and main cutaneous nerves. Source: Mikael Häggström. Public Domain File

Types of dermatomes

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

That dermatome would give sensitivity to the skin of the shoulder, some 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 the middle of the back.

Lumbar dermatomes

They innervate the skin on the lower back, the front area of the legs, the outer thighs, and the top and bottom 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 the calves, as well as the outer edge of the feet.

Distribution of the cutaneous nerves of the sole of the foot. Source: Henry Vandyke Carter, Henry Gray (1918) Anatomy of the Human Body, Public Domain File

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 have 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 Garret map. The second is the 1933 Foerster map. The latter is the most widely used.

The two maps show the progression of limb growth 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.

Keegan and Garrett's map. Grant, John Charles Boileau / Public domain

Clinical significance

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

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 compressing the L5 nerve root results in pain and tingling in the lower leg and foot.

Dermatomes are useful for diagnosing and treating different conditions. The main ones are viral diseases, radiculopathy, and spinal cord injuries.

Viral diseases

There are certain viral diseases that are localized in specific dermatomes, such as herpes zoster. This virus is latent in the spinal cord and when it manifests it moves through the spinal nerve causing a painful rash on the skin that is linked to 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 get into 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, start with the part of the skin that the patient has noticed changes. He will travel it with a pin or a fork on both sides of the body until he reaches the normal sensation.

You can also check if it picks up the vibration along the vertebrae. The sensory level is usually two or three levels below the injury.

Difference with myotomes

Mapping the perception and awareness of visceral sensations in certain regions of the body. Source: User: CFCF, modified by User: RichardWeiss CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) via Wikimedia Commons

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

For example, they are in charge of flexing the thigh, extending the knee or carrying out the extension of the big toe in the lower part of the trunk.

References

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

DERMATOME: WHAT IS IT, TYPES AND CLINICAL SIGNIFICANCE - ANATOMY AND PHYSIOLOGY - 2025