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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”.[1] 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.[2][3]

Spinal nerves arise at different levels of the spinal cord (e.g., C3 and C4). Their ventral rami may contribute to nerve plexuses, such as the brachial and lumbosacral plexuses, where fibres from adjacent roots intermingle to form peripheral nerves, or follow a segmental distribution without forming a plexus, as the thoracic intercostal nerves do.[4] A single nerve root can therefore supply more than one peripheral nerve.[5]

Thirty dermatomes are conventionally described: seven cervical (C2–C8; C1 has no cutaneous dermatome), twelve thoracic, five lumbar, five sacral and one coccygeal[5]. The International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) tests a standardised subset of 28 (C2 to S4–5, with S4–5 taken as one level).[6] Each dermatome is supplied by the dorsal root of a single spinal nerve. Dysfunction or damage to a spinal nerve root from infection, compression, or traumatic injury can trigger symptoms in the corresponding dermatome.

[7]
[8]
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.[9][10][2]

History

The idea of dermatomes originated from initial efforts to associate anatomy with the physiology of sensation.[11] Multiple definitions of dermatomes exist, and several maps are commonly employed. Although they are valuable, dermatomes vary significantly between maps and even among individuals,[11] with some evidence suggesting that current dermatome maps are inaccurate and based on flawed studies.[3] [12]

Two primary dermatome maps have traditionally been recognised in clinical practice.[3] [12] The first is the Keegan and Garrett map (1948), which illustrates dermatomes in alignment with the developmental progression of the limb segments.[13] The second is the Foerster map (1933), which depicts the medial upper limb.[14] 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.[14][2] Keegan and Garrett later refined these maps by examining the segmental distribution of cutaneous nerves in the limbs.[13][2] The Foerster map is featured in the American Spinal Injury Association Impairment Scale (ASIA Scale) for assessing spinal cord injury. Lee et al. systematically reviewed the available evidence, concluded that current dermatome maps are inaccurate and based on flawed studies, and proposed an evidence-based composite map.[3]

Purpose

Testing of dermatomes is part of the neurological examination.[10] 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.[10][6]

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 [6]
  • Pin-prick Test - Pain Sensation - Gently touch the skin with the pin and ask the patient whether it feels sharp or dull[6]

[15]


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.[16]

Adjacent dermatomes overlap substantially, so injury to a single dorsal root does not cause complete loss of sensation in the corresponding area of skin.[2] This overlap is greater for light touch, pressure and vibration than for pain and temperature.[17] Pain (pin-prick) testing therefore provides a more precise assessment of segmental nerve injury than testing with light touch, pressure or vibration.[17]

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 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.[6] 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.[6] See the 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.[12][16]

Clinical Significance

Dermatomes are important because they can help to assess and diagnose a variety of conditions.[2] Dermatomal testing helps clinicians localise the level of a neurological lesion.[2] 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.[18] 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.[6] A dermatomal rash or pain pattern can also support the diagnosis of herpes zoster.[19][20] Dermatomal assessment is relevant in conditions such as:

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[23] or Conus Medullaris Syndrome
  • Rapidly progressing sensory loss
  • Sensory loss following trauma, or with a history of cancer, fever or unexplained weight loss
  • New bladder or bowel dysfunction, or sexual dysfunction[23]

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. ↑ De Luigi AJ, Fitzpatrick KF. Physical examination in radiculopathy. Physical Medicine and Rehabilitation Clinics. 2011 Feb 1;22(1):7-40.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 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.
  3. ↑ 3.0 3.1 3.2 3.3 Lee MW, McPhee RW, Stringer MD. An evidence-based approach to human dermatomes. Australasian Musculoskeletal Medicine. 2013 Jun;18(1):14-22.
  4. ↑ Homma S, Shimada T, Wada I, Kumaki K, Sato N, Yaginuma H. A three-component model of the spinal nerve ramification: Bringing together the human gross anatomy and modern Embryology. Frontiers in Neuroscience. 2023 Jan 16;16:1009542.
  5. ↑ 5.0 5.1 Standring S, editor. Gray's Anatomy E-Book: Gray's Anatomy E-Book. Elsevier Health Sciences; 2021 May 22.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Rupp R, Biering-Sørensen F, Burns S, Franz S, Furlan JC, Guest J, Jones L, Kirshblum S, Krassioukov A, McClure I, Rodriguez G. International Standards for Neurological Classification of Spinal Cord Injury: 2026. Topics in Spinal Cord Injury Rehabilitation. 2026;32(4):141-68.
  7. ↑ Sam Webster. Upper limb dermatomes. Available from: https://www.youtube.com/watch?v=joiuWmTeN0Y [last accessed 15/10/2026]
  8. ↑ Anatomy and Physiology by M. Roehrs. Dermatomes. Available from: https://www.youtube.com/watch?v=CYZBH6NX8wg [last accessed 15/10/2026]
  9. ↑ David J. Magee. Orthopedic Physical Assessment. 6th edition. Elsevier. 2014.
  10. ↑ 10.0 10.1 10.2 10.3 Rupp R, Biering-Sørensen F, Burns SP, Graves DE, Guest J, Jones L, Read MS, Rodriguez GM, Schuld C, Tansey-Md KE, Walden K. International standards for neurological classification of spinal cord injury: revised 2019. Topics in spinal cord injury rehabilitation. 2021 Mar 1;27(2):1-22.
  11. ↑ 11.0 11.1 Apok V, Gurusinghe NT, Mitchell JD, Emsley HC. Dermatomes and dogma. Practical neurology. 2011 Apr;11(2):100-5.
  12. ↑ 12.0 12.1 12.2 Downs MB, Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):427-34.
  13. ↑ 13.0 13.1 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.
  14. ↑ 14.0 14.1 Foerster O. The dermatomes in man. Brain. 1933 Mar 1;56(1):1-39.
  15. ↑ lcdpt2015. Dermatome Screening Jon, Drew, Juliana. Available from: https://www.youtube.com/watch?v=ETvKVAYxKO0 [last accessed 15/10/2026]
  16. ↑ 16.0 16.1 O'sullivan SB, Schmitz TJ, Fulk G. Physical rehabilitation. FA Davis; 2019 Jan 25.
  17. ↑ 17.0 17.1 Khoo YH, AbdullAh JM, IdrIs Z, GhAnI AR, Halim SA. Dorsal column bedside examination test: tips for the neurosurgical resident. The Malaysian Journal of Medical Sciences: MJMS. 2023 Apr 18;30(2):172.
  18. ↑ Robblee J, Katzberg H. Distinguishing radiculopathies from mononeuropathies. Frontiers in Neurology. 2016 Jul 13;7:111.
  19. ↑ 19.0 19.1 Centers for Disease Control and Prevention (CDC). Clinical Features of Shingles (Herpes Zoster) [Internet]. CDC; 2024
  20. ↑ Aurangzeb A, Chong EY, Yuen PW, Koh DT, Kuo CL. Case Report of Herpes Zoster Infection of the Cervical Dermatome–A Rare Cause of Acute Shoulder Pain. Journal of Orthopaedic Case Reports. 2024 Aug;14(8):89.
  21. ↑ Schmid AB, Fundaun J, Tampin B. Entrapment neuropathies: a contemporary approach to pathophysiology, clinical assessment, and management. Pain reports. 2020 Jul 22;5(4):e829.
  22. ↑ Soar H, Comer C, Wilby MJ, Baranidharan G. Lumbar radicular pain. BJA education. 2022 Sep 1;22(9):343-9.
  23. ↑ 23.0 23.1 Conte A, Jain R, Lingham A, Mueller M. Cauda Equina Syndrome—A 2025 Narrative Review. British Journal of Hospital Medicine. 2026 Apr 16;87(4).
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