What Are They, Related Diseases, and More
Editors:Alyssa Haag,Ian Mannarino, MD, MBA,Kelsey LaFayette, DNP, RN, FNP-C
Illustrator:Jessica Reynolds, MS
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What are dermatomes?
A dermatome refers to an area of skin supplied and innervated by a single spinal nerve root. Spinal nerves are part of the peripheral nervous system (PNS) and form nerve roots that branch from the spinal cord. Spinal nerves are grouped by the region of the spine they’re associated with, resulting in 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal spinal nerve roots. In total, there are 31 pairs of spinal nerves and 30 dermatomes total as there is no dermatome for the first cervical (C1) spinal level. The dermatomes can vary slightly from person to person.
Where are dermatomes located?
The cervical nerves, numbered C1 to C8, originate from the neck and mainly supply the dermatomes of the neck and arms. Specifically, the C2 and C3 dermatomes supply the crown and posterior scalp, anterior neck, the base of the skull, and the ear lobes. The C4 spinal nerve supplies the skin over parts of the neck, the tips of the shoulders, and upper arms. C5 covers the lateral upper arm to the elbow. C6 covers the thumb of the hand and lateral forearm. C7 covers the shoulders, posterior arms, and the middle finger. C8 covers the pinky of the hand and the medial forearm.
The thoracic nerves, T1 to T12, originate from the part of the spine that makes up the torso and supply dermatomes located on the chest, abdomen, arms, and mid-back. T1 supplies the upper chest and back, axilla, and medial aspect of the upper arm. T2 and T3 cover the upper chest and back. T4 innervates the area approximately at the level of the nipples and the back. The rest of the thoracic dermatomes cover the abdomen and mid-back, traveling inferiorly/caudally with T10 notably innervating the area of the umbilicus.
The lumbar nerves, L1 to L5, originate from the spine of the lower back and supply the skin of the legs. Specifically, L1 innervates the groin, upper trochanter (or outer hips), and lower back. L2 innervates the back, hips, and anterior thighs. L3 innervates the back, upper buttock, and the medial thigh and legs to the knees. L4 innervates the back, the anterior thigh and calf, posterior knees, medial ankle, and the heels. L5 innervates the back; anterior and lateral calf; and the feet, including the first four toes.
The sacral nerves, S1 to S5, are associated with the sacrum, a bone found in the pelvis. S1 mainly supplies the buttocks and posterolateral aspect of the leg. S2 supplies the buttock and posteromedial aspect of the leg. S3 supplies the buttock and genitals. Lastly, S4 and S5 supply the perineal area, which include the genitals.spinal nerves are the coccygeal nerves, which emerge from the conus medullaris, the termination of the spinal cord. It serves to innervate the 30th dermatome, which covers the area of skin overlying the tailbone (coccyx).
Can dermatomes be assessed or tested?
Dermatomes can be assessed or tested as a component of the neurological examination to assess for radiculopathy, or spinal nerve root injury. Dermatome testing is also commonly used when assessing the level of spinal anesthesia. A pinprick test is used to test for pain sensation. The clinician will gently touch the skin with a pin and ask the individual if they feel any sensation and if the sensation is sharp or dull. The clinician will proceed to do this in a systematic manner over the 30 dermatomes to test for nerve damage at any spinal level. In addition to the pinprick test, they may also perform a light touch test where they dab a piece of cotton wool on a small area of the body. Similarly, this is done for each dermatome to assess for deficits in light touch sensitivity, which can indicate nerve damage.
What disease(s) affect dermatomes?
Diseases affecting the dermatomes include radiculopathies, which refers to a condition where the nerve root exiting the spinal cord becomes compressed or pinched. This can occur as a result of increased age or trauma to the back, such as a motor vehicle accident. Disc herniation is a common cause of radiculopathy where the intervertebral disc serving as a protective cushion between each spinal vertebrae bulges and compresses the surrounding nerve. This may cause pain, weakness, and tingling sensations that can affect one or many dermatomes.Shingles, a reactivation of the varicella zoster (i.e., chickenpox) virus, is another disease that affects dermatomes. If varicella zoster is contracted at a young age, the virus may lie dormant in the body for several years. When it is reactivated, it often affects only a single nerve root and causes pain and a distinct rash that spreads over one dermatome. This causes a characteristic itching, burning, or tingling in only one area of the skin, typically the chest and back, on only one side of the body (i.e. the thoracic dermatomes).
What are the most important facts to know about dermatomes?
A dermatome is an area of skin innervated by a specific spinal nerve root. There are 30 dermatomes in total, divided into the cervical, thoracic, lumbar, sacral, and coccygeal levels. There are eight cervical levels total that cover the skin that span the scalp to the arms. There are 12 thoracic levels covering the arms, chest, abdomen, and middle of the back. The five lumbar levels course down the anterior and posterior legs as well as the feet. The five sacral spinal nerves mainly innervate the groin area, including the buttock and genitals as well as the lower extremities. The last coccygeal spinal nerve innervates the tailbone. Dermatomes are characteristically affected in radiculopathies and in shingles. Radiculopathies are commonly due to disc herniations as a result of advanced age or trauma, whereas shingles is caused by the reactivation of the varicella zoster virus. Assessment of the dermatomes are conducted in a neurological examination and typically includes a pinprick test and a light touch test.
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Related linksIntroduction to the central and peripheral nervous systems
Development of the axial skeleton
Resources for research and reference
Coccygeal nerve. In Science Direct. Retrieved May 9, 2022, from https://www.sciencedirect.com/topics/neuroscience/coccygeal-nerve
Dickerman, R. (2019). The C1-C2 vertebrae and spinal segment. In Spine-Health. Retrieved May 9, 2022, from https://www.spine-health.com/conditions/spine-anatomy/c1-c2-vertebrae-and-spinal-segment
Poletti, C. E. (1991). C2 and C3 pain dermatomes in man. Cephalalgia, 11(3): 155-159. DOI: 10.1046/j.1468-2982.1991.1103155.xSingh, V. (2021). Textbook of clinical neuroanatomy (4th ed.). New Delhi Haryana, India. Elsevier.