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Dermatomes

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Dermatomes

The term “dermatome” is a combination of two Greek words; “derma” meaning “skin”, and “tome”, meaning “cutting” or “thin segment”. Dermatomes are areas of the skin whose sensory distribution is innervated by the afferent nerve fibres from the dorsal root of a specific single spinal nerve root, which is that portion of a peripheral nerve that “connects” the nerve to the spinal cord.

Nerve roots arise from each level of the spinal cord (e.g., C3, C4), and many, but not all, intermingle in a plexus (brachial, lumbar, or lumbosacral) to form different peripheral nerves. This arrangement can result in a single nerve root supplying more than one peripheral nerve. For example, the median nerve is derived from the C6, C7, C8, and T1 Nerve Roots, whereas the ulnar nerve is derived from C7, C8, and T1.

In total there are 30 conventionally described dermatomes that relay sensation from a particular region of the skin to the brain - 8 cervical nerves (note C1 has no cutaneous dermatome), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each dermatome is supplied by the dorsal root of a single spinal nerve.[1] Dysfunction or damage to a spinal nerve root from infection, compression, or traumatic injury can trigger symptoms in the corresponding dermatome. [2]

[3]
[4]
Table 1. Dermatomes
Nerve Root Dermatome
Cervical C2 Supply Skin of Neck Temple, Forehead, Occiput
C3 Entire Neck, Posterior Cheek, Temporal Area, Prolongation forward under Mandible
C4 Shoulder Area, Clavicular Area, Upper Scapular Area
C5 Supply the Arms  Deltoid Area, Anterior aspect of entire arm to base of thumb
C6 Anterior Arm, Radial side of hand to thumb and index finger
C7 Lateral Arm and Forearm to index, long, and ring fingers
C8 Medial Arm and forearm to long, ring, and little fingers
Thoracic T1 Medial side of forearm to base of little finger
T2 Supply the chest and abdomen Medial side of upper arm to medial elbow, pectoral and midscapular areas
T3 - 6 Upper Thorax
T5 - 7 Costal Margin
T8 - 12 Abdomen and Lumbar Region
Lumbar L1 Back, over trochanter and groin
L2 Back, front of thigh to knee
L3 Supply Skin of Legs Back, upper buttock, anterior thigh and knee, medial lower leg
L4 Medial buttock, lateral thigh, medial leg, dorsum of foot, big toe
L5 Buttock, posterior and lateral thigh, lateral aspect of leg, dorsum of foot, medial half of sole, first, second, and third toes
Sacral S1 Buttock, Thigh, and Leg Posterior
S2 Supply Groin Same as S1
S3 Groin, medial thigh to knee
S4 Perineum, genitals, lower sacrum
Coccygeal The dermatome corresponding with the coccygeal nerves is located on the buttocks, in the area directly around the coccyx.[5][6]

History

The idea of dermatomes originated from initial efforts to associate anatomy with the physiology of sensation.[7] Multiple definitions of dermatomes exist, and several maps are commonly employed. Although they are valuable, dermatomes vary significantly between maps and even among individuals,[7] with some evidence suggesting that current dermatome maps are inaccurate and based on flawed studies.[8] [9]

Two primary dermatome maps have traditionally been recognised in clinical practice..[8] [9] The first is the Keegan and Garrett map (1948), which illustrates dermatomes in alignment with the developmental progression of the limb segments.[10] The second is the Foerster map (1933), which depicts the medial upper limb as innervated by T1-T3.[11] Foerster used rhizotomy, the surgical section of dorsal nerve roots, to study sensory loss in individual dermatomes, and his work became the foundation of modern dermatome maps.[11][12] Keegan and Garrett later refined these maps by examining the segmental distribution of cutaneous nerves in the limbs.[10][12] The Foerster map is featured in the American Spinal Cord Injury Association Impairment Scale (ASIA Scale) for assessing spinal cord injury. In recent years there have been few attempts at verifying these original dermatome maps. Lee et al. conducted an in-depth review that examined the discrepancies among dermatome maps. They put forth an “evidence-based” dermatome map that combined elements of previous maps (Fig.3). Though the application of the term “evidence-based” may be somewhat questionable, their proposed map represents a systematic attempt to synthesise the most credible evidence available.[7][8]

Purpose

Testing of dermatomes is part of the neurological examination. They are primarily used to determine whether the sensory loss on a limb corresponds to a single spinal segment, implying the lesion is of that nerve root (i.e., radiculopathy), and to assign the neurologic “level” to a spinal cord lesion[13].

Technique

Dermatome testing is ideally done with a pin and cotton wool. Ask the patient to close their eyes and give the therapist feedback regarding the various stimuli. Testing should be done on specific dermatomes and should be compared bilaterally.

  • Light Touch Test - Light Touch Sensation - Lightly touch the skin with cotton wool [14]
  • Pin-prick Test - Pain Sensation - Gently touch the skin with the pin and ask the patient whether it feels sharp or blunt


During the review of systems, asking the patient to carefully describe the pattern or distribution of sensory symptoms (e.g., tingling, numbness, diminished, or absent sensation) provides the therapist with preliminary information to help guide the examination and to assist in identifying the dermatome(s) and nerve(s) involved.[15]

Light touch dermatomes are larger than pain dermatomes. When only one or two segments are affected, testing for pain sensibility is a more sensitive method of examination than testing for light touch.[13]

Anterior and posterior body outlines divided into shaded bands, each labelled with a spinal nerve level to show dermatome distribution from the neck to the feet.
Figure 1. Dermatome map from Grant’s An Atlas of Anatomy (1962), showing the segmental distribution of cutaneous innervation by spinal nerve level on the anterior and posterior body surface

Scoring

The International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) test light touch and pin-prick sensation at a standardised key sensory point in 28 dermatomes (C2 to S4-5) on each side of the body.[16] Each point is scored 0 (absent), 1 (impaired) or 2 (normal), or “NT” if not testable. The sensory level is the most caudal dermatome with intact sensation. Sensation at S4-5 is key to distinguishing complete from incomplete injury. See the American Spinal Injury Association (ASIA) page for full scoring and classification.

Controversies

Dermatomes have a segmented distribution throughout the body. The exact dermatome pattern can actually vary from person to person. Some overlap between neighbouring dermatomes may also occur. There exist some discrepancies among published dermatome maps based on the methodologies used to identify skin segment innervation..

In a clinical commentary, Downs and Laporte discuss the history of dermatome mapping, including the variations in methodologies employed, and the inconsistencies in the dermatome maps used in education and practice.[15][17]

[18]

Clinical Significance

Dermatomes are important because they can help to assess and diagnose a variety of conditions. Dermatomal testing helps clinicians localise the level of a neurological lesion. Sensory loss in a single dermatomal distribution suggests nerve root involvement (radiculopathy), whereas loss in a peripheral cutaneous nerve distribution points to a peripheral nerve lesion. Distinguishing between the two supports clinical reasoning and assessment. Findings are interpreted alongside myotomes and reflexes rather than in isolation. In spinal cord injury, dermatomal testing determines the sensory level and contributes to injury classification and prognosis. A dermatomal rash or pain pattern can also support the diagnosis of herpes zoster.

Red Flags

Some sensory findings need urgent medical referral rather than routine management:

  • Saddle (perineal) anaesthesia: altered sensation in the S2–S5 dermatomes (perineum, genitals, and perianal area), which may indicate Cauda Equina Syndrome or Conus Medullaris Syndrome
  • Sensory loss following trauma, or with a history of cancer, fever or unexplained weight loss
  • New bladder or bowel dysfunction, or sexual dysfunction

Although some of these features are not routinely examined in an outpatient assessment, it is important to ask about them in the subjective history to help identify serious pathology early and ensure timely referral.

References

  1. ↑ Wikipedia Dermatome. Available from: https://en.wikipedia.org/wiki/Dermatome_(anatomy) (last accessed 23.4.2019)
  2. ↑ 2.0 2.1 Medical news today What and where are dermatomes? Available:https://www.medicalnewstoday.com/articles/what-are-dermatomes (accessed 25.5.2022)
  3. ↑ Sam Webster. Upper limb dermatomes. Available from: https://www.youtube.com/watch?v=joiuWmTeN0Y [last accessed 15/10/2026]
  4. ↑ Anatomy and Physiology by M. Roehrs. Dermatomes. Available from: https://www.youtube.com/watch?v=CYZBH6NX8wg [last accessed 15/10/2026]
  5. ↑ Medical news today What and where are dermatomes? Available:https://www.medicalnewstoday.com/articles/what-are-dermatomes (accessed 25.5.2022)
  6. ↑ David J. Magee. Orthopedic Physical Assessment. 6th edition. Elsevier. 2014.
  7. ↑ 7.0 7.1 7.2 Apok V, Gurusinghe NT, Mitchell JD, Emsley HC. Dermatomes and dogma. Practical neurology. 2011 Apr 1;11(2):100-5.
  8. ↑ 8.0 8.1 8.2 Lee MW, McPhee RW, Stringer MD. An evidence-based approach to human dermatomes. Australasian Musculoskeletal Medicine. 2013 Jun;18(1):14-22.
  9. ↑ 9.0 9.1 Downs MB, Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):427-34.
  10. ↑ 10.0 10.1 Keegan JJ, Garrett FD. The segmental distribution of the cutaneous nerves in the limbs of man. The Anatomical Record. 1948 Dec;102(4):409-37.
  11. ↑ 11.0 11.1 Foerster O. The dermatomes in man. Brain. 1933 Mar 1;56(1):1-39.
  12. ↑ 12.0 12.1 Rajendran B, Yunos MA, Nagalinggam H, Aziz ML, Abdullah JM. Surface Anatomy and Sensory Evaluation of Dermatomes: A Guide for Residents. The Malaysian Journal of Medical Sciences: MJMS. 2025 Feb 28;32(1):169.
  13. ↑ 13.0 13.1 Liebenson C, editor. Rehabilitation of the spine: a practitioner's manual. Lippincott Williams & Wilkins; 2007.Available: https://www.sciencedirect.com/topics/medicine-and-dentistry/dermatome (accessed 25.5.2022)
  14. ↑ Slide share. Dermatomes and myotomes. Available from: https://www.slideshare.net/TafzzSailo/special-test-for-dermatomes-and-myotomes (last accessed 23.4.2019)
  15. ↑ 15.0 15.1 Susan B.O'Sullivan, Thomas J. Schmitz, George D. Fulk. Physical Rehabilitation. 6th edition. F. A. Davis Company. 2014.
  16. ↑ Biering-Sørensen F, Burns SP, Graves DE, Guest J, Jones L, Read MS, Rodriguez GM, Schuld C, Walden K, Kirshblum S. International standards for neurological classification of spinal cord injury. Topics In Spinal Cord Injury Rehabilitation. 2021 Mar 1;27(2):1-22.
  17. ↑ Downs MB, Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):427-34.
  18. ↑ lcdpt2015. Dermatome Screening Jon, Drew, Juliana. Available from: https://www.youtube.com/watch?v=ETvKVAYxKO0 [last accessed 15/10/2026]
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