A dermatome is an area of skin supplied by a single spinal nerve. Problems in a specific dermatome can indicate problems with the corresponding nerve root in the spine.
Examples of dermatomes are as follows:
- Numbness and tingling down the right arm to the thumb and middle finger may involve C6-C8 dermatomes and indicate abnormalities in the spinal nerves of the C6-C8 nerve roots, whether in the vertebrae, spinal cord, or discs.
- Sciatica pain that starts from the hip and travels down the back of the thigh to the knee may involve the S1 or S2 dermatomes and indicate a problem with the nerve that comes out below the first sacral spinal nerves.
Where are dermatomes located?
In order to understand dermatomes, it’s important to understand how spinal nerves function. Spinal nerves are part of the peripheral nervous system (PNS)., whose main function is to connect the brain to the rest of the body so that the brain can evaluate sensory input.
The body has 31 pairs of spinal nerves that are named and grouped according to the corresponding area of the spine:
- Cervical nerves (C1-C8): 8 pairs located in the neck
- Thoracic nerves (T1-T2): 12 pairs located in the torso
- Lumbar nerves (L1-L5): 5 pairs located in the lower back
- Sacral nerve (S1-S5): 5 pairs located in the sacrum or pelvis
- Coccygeal nerves: 1 pair located in the coccyx or tailbone
Except for C1, there are dermatomes for each spinal nerve, totaling 30. Dermatomes form a combination of horizontal layers in the upper body, giving an appearance of a stacked disc. In the legs, dermatomes run vertically due to the shape of the legs.
|Cervical spinal nerves||Location of dermatomes|
|C2||Base of the skull behind the ear|
|C3||Back of the head and upper neck|
|C4||Lower neck and upper shoulders|
|C5||Upper shoulders and collarbones|
|C6||Thumb, index fingers, and upper forearm|
|C7||Middle finger, back of the arms, and upper back|
|C8||Little finger, ring fingers, inner arms, and upper back|
|Thoracic spinal nerves||Location of dermatomes|
|T1||Upper chest, back, and inner forearm|
|T2||Upper inner arm|
|T3||Middle of the back (dorsal)|
|T4||Upper chest and back|
|T5||Bottom of the foot|
|T7||Mid-chest and back|
|T8||Upper abdomen and mid-back|
|T9||Upper abdomen and mid-back|
|T10||Abdomen (belly button area) and mid-back|
|T11||Abdomen and mid-back|
|T12||Lower abdomen and mid-back|
|Lumbar spinal nerves||Location of dermatomes|
|L1||Lower back, hips, and groin|
|L2||Lower back, front and inside of the thigh|
|L3||Lower back, front and inside of the thigh|
|L4||Lower back, front of thigh and calf, knee area, and inside of the ankle|
|L5||Lower back, front and outside of the calf, top and bottom of the foot, and first 4 toes|
|Sacral spinal nerves||Location of the dermatomes|
|S1||Lower back, back of the thigh, back and inside of the calf, and pinky toe|
|S2||Buttocks, genitals, and back of the thigh and calf|
|S3||Buttocks and genitals|
|Coccygeal spinal nerves||Location of the dermatomes|
|Buttocks and tailbone area|
What conditions can be diagnosed with the help of dermatomes?
Dermatomes can help diagnose medical conditions as they are located in the same area in almost every human. Conditions commonly diagnosed with the help of dermatomes include:
- Herpes zoster (shingles): Shingles is a viral infection caused by the varicella-zoster virus, which may remain dormant in a particular nerve root. Viral reactivation can cause rash and pain along the corresponding dermatome.
- Lumbar radiculopathy: Lumbar radiculopathy is a condition in which the spinal nerve root gets compressed, leading to radiating back pain, weakness, and tingling that extends down a dermatome.
- Spinal cord trauma: Dermatomes can be used to evaluate and diagnose the exact level of the spinal cord or nerve injury in patients who had an accident.
What is the difference between dermatomes and myotomes?
The major difference between a dermatome and myotomes is their location and type of nerve supply:
- Dermatomes are areas on the skin supplied by a particular sensory spinal nerve
- Myotomes originate from a group of muscles supplied by a single spinal motor nerve.
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