A dermatome is the area of skin supplied by the sensory fibres of a single spinal nerve root. Because those areas follow a broadly predictable pattern, the distribution of a patient's numbness, tingling, or pain is often the fastest clue to which nerve root is involved.
This reference pairs each level from C2 to S5 with its ASIA key sensory point — the single, reproducible spot used in the International Standards for Neurological Classification of Spinal Cord Injury — along with the myotome and deep tendon reflex that share the level, so a sensory finding can be corroborated with a motor one.
Zdrovia — https://www.zdrovia.ca/resources/dermatome-map/
Dermatome Reference
Spinal Level & Dermatome Lookup
Select a level for its ASIA key sensory point, cutaneous distribution, matched myotome and reflex — or start from where the symptoms are.
C1 is omitted — it has no meaningful cutaneous distribution.
Start from the symptoms instead
Level C6
Upper limbASIA key sensory point
Thumb
Tested for light touch and pin prick, both sides
Cutaneous distribution
Lateral forearm, thumb and index finger
Myotome
Wrist extension
Reflex
Brachioradialis
These results are estimates based on published clinical data and are for informational purposes only. They do not constitute medical advice, a diagnosis, or a treatment recommendation. Consult a licensed aesthetic practitioner before beginning any treatment. Individual results vary.
Zdrovia's smart blocks drop a dermatome finding straight into the chart note, so the sensory level is documented while you're still with the patient. See how smart blocks work →
Document the level you just mapped
Zdrovia's smart blocks drop a dermatome finding straight into the chart note, so the sensory level is documented while you're still with the patient.
How to use a dermatome map in assessment
Dermatomes are most useful for localisation, not diagnosis. A patient reporting numbness over the thumb and lateral forearm points toward C6; numbness over the little finger points toward C8. Confirming with the matched myotome (C6 wrist extension, C8 finger flexion) and reflex (C6 brachioradialis) turns a single soft finding into a pattern.
The boundaries drawn on any dermatome chart are a convenient fiction. Adjacent dermatomes overlap substantially — often enough that a single root lesion produces a smaller sensory deficit than the map predicts, or none at all. Published maps also disagree with one another, particularly over the limbs, because they were derived by different methods.
This is why the ASIA standards test one key point per level rather than a whole region. A single reproducible landmark, tested for light touch and pin prick, is far more consistent between examiners than asking someone to outline an area on a diagram.
Dermatomes and shingles
Herpes zoster reactivates in a single dorsal root ganglion, so the rash typically erupts in one dermatome on one side of the body and stops abruptly at the midline. That unilateral, single-band distribution is characteristic enough to be diagnostic on its own in most cases.
Thoracic levels are the most commonly affected, followed by the ophthalmic division of the trigeminal nerve. A rash crossing the midline, or spanning several non-adjacent dermatomes, suggests something other than uncomplicated zoster and warrants a closer look — disseminated zoster in particular is associated with immunosuppression.
Dermatomes vs. myotomes vs. peripheral nerves
A dermatome maps a nerve root to skin sensation; a myotome maps a nerve root to muscle action. A peripheral nerve is a different thing again — it carries fibres from several roots, so a peripheral nerve lesion produces a sensory pattern that does not respect dermatome boundaries at all.
That distinction is often what the assessment turns on. Numbness in the thumb, index, and middle fingers that stops at the wrist crease suggests median nerve compression at the carpal tunnel. Numbness in the thumb that extends up the lateral forearm suggests a C6 root. The complaint sounds similar; the map tells them apart.