Dermatomes are areas of skin that are primarily supplied by a single spinal nerve. There are 8 cervical nerves (note that C1 has no dermatome), 12 thoracic nerves, 5 lumbar nerves, and 5 sacral nerves. Each of these spinal nerves transmits sensation from a specific area of the skin to the brain. [1]
Spinal nerve dysfunction or damage can trigger symptoms in the corresponding dermatome. Infectious compression or trauma may lead to nerve damage or dysfunction [2].
Nerve Roots Dermatomes
| Name | cervical | thoracic | lumbar | sacral |
|---|---|---|---|---|
C2-C8 | C2 Temple forehead occipital
/ C3 whole neck posterior cheek temporal region forward extension mandible// C4 shoulder region upper part of clavicle Scapular region// C5 Deltoid region Whole | T1 Medial forearm to base of little finger Fingers T2 medial upper arm to medial elbow chest and mid-scapula T3-T12 T3-T6 upper thorax; T5-T7 costal border; T8-T12 abdomen and lumbar lumbar spine front of arm to base of thumb//// C6 Front of arm radial to thumb and index finger// C7 Outside arm and forearm to index finger and ring finger //C8 Inside arm and forearm to long ring and little finger Chest | LUMBAR spine L1 back in greater trochanter and groin L2 front of thigh to knee L3 upper back buttocks Front thigh and lower inner knee Leg L4 inner buttocks outer thigh inner calf dorsum of foot big toe L5 back of buttocks and outer thigh dorsal inner leg first second and third toes inner half sacrum | sacrum S1 hip thigh and back of leg /S2 same as S1 / S3 groin thigh Medial to knee / S4 perineal subgenital sacrum |
Purpose
Dermatological examination is part of the neurological examination. They are primarily used to determine if sensory loss on a limb corresponds to a single spinal segment, imply that the lesion belongs to that nerve root (i.e. radiculopathy), and assign nerve “levels” to the spine Spinal cord injury [6].
Technique
Ideally, use needles and cotton wool for dermatological testing. Ask the patient to close their eyes and provide feedback to the therapist on various stimuli. Testing should be performed on specific dermatomes and should be compared bilaterally.
- Needle prick test (pain sensation) – gently touch the skin with a needle and ask the patient if it feels sharp or dull
- Light touch test (light touch) – dab a piece of lint on the skin area [7]
During the systematic review process
, the patient is asked to carefully describe the pattern or distribution of sensory symptoms (eg, decreased tingling, numbness, or sensory loss) to provide the therapist with initial information to help guide the examination and help identify The dermatomes and nerves involved. [8]
Tactile dermatomes are larger than pain dermatomes. Pain sensitivity testing is a more sensitive test than abnormal touch testing when only one or two segments are affected. [6]
Peripheral nerve injury
Peripheral nerve injury usually presents with sensory disturbances parallel to the distribution of the affected nerve and corresponding to its innervation pattern. E.g
- If the patient complains of ulnar numbness in the ulnar half of the ring finger, the little finger, and the hand, the therapist is reminded to carefully manage the integrity of the ulnar nerves (C8 and T1) during the sensory examination.
- Complaints of sensory disturbances on the palmar surface of the thumb, index finger, middle finger, and ring finger on the radial half palm and distal dorsal surface suggest involvement of the median nerves (C6-8 and T1).
here are some differences between the published dermatomograms based on the method used to identify the innervation of skin segments. In a clinical review, Downs and Laporte discuss the history of skin area mapping, including changes in methods used and Skin slice diagram for education and practice. [8][[Laporte C. Conflicting skin slices: educational and clinical implications. Journal of Orthopedics and Sports Physical Therapy. 2011 Jun;41(6):42[9]7-34.]]
Associated Health Conditions
Symptoms within the dermatome sometimes indicate damage or disruption of the corresponding nerve in the dermatome. The location of these symptoms can help diagnose certain underlying medical conditions. E.g
- Shingles/Herpes Zoster
- Spinal Cord Injury
- Pinched Nerve/Nerve entrapment[2]
References
1.↑ Wikipedia Dermatology. Available from: https://en.wikipedia.org/wiki/Dermatome_(anatomy) (last accessed 23.4.2019) ↑ Jump to:
2. 2.0 2.1 2.2 Today’s Medical News What is a Dermatome and Where? Available: https://www.medicalnewstoday.com/articles/what-are-dermatomes (accessed 25 May 2022)
3.↑ M Rawls. skin festival. Available at: https://www.youtube.com/watch?v=CYZBH6NX8wg&feature=youtu.be (last accessed 23.4.2019)
4.↑ Overview of Dermatology – © Kenhub – Illustrator: Irina Münstermann https:/ /www.kenhub.com/en/library/anatomy/dermatomes
5. ↑ David J. Magee. Orthopedic Physics Evaluate. 6th edition. Elsevier. 2014.
6.↑ Jump to: 6.0 6.1 Liebenson C Editor. Spinal Rehabilitation: A Practitioner’s Manual. Lippincott, Williams and Wilkins; 2007. Available: https://www.sciencedirect.com/topics/medicine-and-dentistry/dermatome (accessed 25 May 2022)
7.↑ Slides share. Dermatomes and sarcomeres. Available from: https://www.slideshare.net/TafzzSailo/special-test-for-dermatomes-and-myotomes (last accessed 23.4.2019)
8.↑ Jump to: 8.0 8.1 8.2 Susan B.O’Sullivan Thomas J. Schmitz George D. Falk. Physical recovery. 6th edition. F.A. Davis Co. 2014.
9.↑ Downs MB Laporte C. The dermatomal map of conflict: educational and clinical implications. Journal of Orthopedics and Sports Physical Therapy. 2011 Jun;41(6):427-34.
