An improved understanding of the human body and the way our nerves supply us with feedback, about both the outside world and the inner workings of our biology, can help patients recognize why and how they’re feeling pain, and what their treatments and therapies are trying to achieve. When mapping and tracing origins of pain, the dermatome chart plays an important role in the diagnostic process.
Skin is your body’s largest, most important sensory organ. If you feel pain in a particular area, basic anatomy can tell us what nerves supply that area, and provides why pain is being perceived there without an immediately noticeable cause. Often times, when an area feels painful without any indication of damage, there is rooted damage to the nerves in or around the area. This is where the dermatome chart becomes an essential diagnostic tool for spine specialists, doctors and patients alike.
What Are Dermatomes?
Derived from two Greek root words in “derma” (skin) and “tomos” (a slice), dermatomes refers to a section of skin supplied by a spinal nerve, starting with the cervical spine (in the neck) down to the sacrum (the base of our pelvis). These areas are not perfectly exact, and multiple nerves may innervate a single general area. But this guide does provide a general overview of what nerve may be responsible for pain or lack thereof, and helps us better assess and diagnose spinal injury.
The spine is divided into 33 vertebrae, 31 of which have corresponding nerve pairs that innervate specific sections of the body. Of these, 30 are linked to corresponding dermatomes. The topmost cervical nerve attached to the C1 does not have a corresponding dermatome (it helps control neck and head movement, along with the other cervical nerves). The spinal nerves and their corresponding dermatomes are as follows:
- (Cervical) C2 – forehead, and temple
- C3 – neck, posterior cheek
- C4 – shoulders, clavicle, upper shoulder blade
- C5 – deltoids, anterior arm (facing forward) down to the base of the thumb
- C6 – anterior arm as well as the radial side of the hand
- C7 – lateral arm and forearm (facing away from the center) to index, middle, and ring finger
- C8 – medial arm and forearm (facing toward the center) to the middle, ring, and little finger
- (Thoracic) T1 – medial (inner) side of the forearm to the base of the little finger
- T2 – medial (inner) side of the upper arm to the elbow, pectoral muscles (chest) and mid scapular area (between shoulder blades)
- T3-T6 – upper torso
- T5-T7 – costal margin (the portion of skin along the lower side of the ribs)
- T8-T12 – abdomen and lower back
- (Lumbar) L1 – lower back, side of the hip (trochanter), and groin
- L2 – back, front of the thigh (quadriceps) to knee
- L3 – back, upper buttock, front of thigh and knee, inner lower leg (the medial portion of the calves)
- L4 – inner buttock, lateral thigh, inner thigh, dorsal (top) side of the foot, the big toe
- L5 – buttocks, posterior (back) and lateral thigh, lateral side of the entire leg, top of foot, medial (inner) side of the sole, toes
- (Sacral) S1-S2 – buttocks, thighs, and backside of the legs
- S3 – groin, inner thigh
- S4 – perineum and genitals
Not included in the list above is the face, which is innervated by the trigeminal nerve, which is a set of cranial nerves rather than a spinal nerve. Note that the dermatomes of the face are still dermatomes, but because they aren’t innervated by spinal nerves as the rest of the body is, they are not affected by spinal injury and diseases of the spinal cord.
When visualizing dermatomes, it helps to think of the body’s skin as divided into a long series of rings encompassing us from head to toe, with each spinal nerve corresponding to a ring of skin, with certain exemptions.
All dermatomes, save for those of the face, are divided between the four major sections of the spine. When utilizing dermatomes as a diagnostic tool, being able to identify clearly where it hurts or recognizing when a specific dermatome feels numb or unresponsive can help doctors narrow down the potential culprit along the spine, and figure out an effective treatment.
Using Dermatomes as a Diagnostic Tool
The spinal column is composed of a series of tough bones, made flexible by intersecting spongy discs. The spinal cord runs through our spine, connecting to dozens of nerve roots that correspond to a set of nerves throughout the body.
Alongside the brain, the spinal cord is one of the major dividing sections of our central nervous system, coordinating with our ganglia and various nerves throughout the body (our peripheral nervous system, which includes the autonomic, enteric, sympathetic, and parasympathetic nervous systems) to regulate and manage nearly all of the body’s processes, from the release of certain chemicals to the contracting and relaxing of skeletal muscles like those in the leg, smooth muscles like those in our digestive and respiratory tracts, and the automatic pumping function of the heart.
When damage, disease, or infection leads to destroyed cells in the spine or pressure along nerve roots in the spinal cord, the pain can radiate throughout portions of the body that aren’t superficially related to the back, such as the legs, chest, and arms. Tingling feelings, sharp or burning pain, recurring aches, loss of strength, and other symptoms and sensations on the skin and in the muscles can be a sign of damage along the spine.
The Dermatome Chart Role in Evaluating and Diagnosing Conditions
The dermatome chart often play an important role in figuring out where the damage is coming from, giving doctors a hint as to where to check for signs of infection, swelling, or injury. Common diseases that may be partially identified through the dermatome chart include:
A series of other diagnostic tools and symptoms are important for identifying injuries and diseases of the spine, including paralysis, bladder dysfunction, and gait disturbance, as well as diagnostic processes such as imaging (MRI, CT, X-rays checking for bone damage) and blood tests (to check for infection).
Dermatomes play an important role in our understanding of the human body and can help patients better understand how damage to their back can be identified through various symptoms of pain and other strange or out-of-place sensations.
When the spine is damaged, treatments often include medication and intervention to reduce and combat swelling and inflammation, rest and exercise to reduce pain and strengthen the surrounding muscles, and in certain cases, surgery to remove bone spurs or fragments, or decompress a nerve root/the spinal cord.