Nerve
Dermatomes
Overlapping skin regions linked to spinal sensory roots
High-yield
A sensory pattern can help localize a root or peripheral nerve problem, but a map alone cannot make the diagnosis. Compare sensation with muscle strength, reflexes and the rest of the examination.
Overview
A dermatome describes the skin territory associated with one spinal sensory root. Adjacent territories overlap and vary between people. A named peripheral nerve has a different distribution because plexuses combine fibers from several roots; its skin borders can also overlap with neighboring nerves.
Reference facts
- Origin
- Peripheral sensory fibers whose cell bodies lie in the dorsal root ganglion of the corresponding spinal segment
- Root value
- Maps usually begin at C2 and continue through the sacral and coccygeal levels; C1 has no usual discrete skin territory
- Course
- Cutaneous branches of dorsal and ventral rami reach the skin; limb plexuses redistribute ventral-ramus fibers into named peripheral nerves
- Motor
- Dermatomes describe sensation, while myotomes describe segmental muscle function. Common reflex associations include biceps/brachioradialis C5–C6, triceps mainly C7, patellar L2–L4 and Achilles mainly S1
- Sensory
- Approximate reference sites include C6 thumb, C7 middle finger, C8 little finger, T4 nipple level, T10 umbilicus, L3 medial knee, L4 medial malleolus, L5 dorsal great-toe region and S1 lateral foot/ankle
Mnemonic
Useful starting points: C6 thumb, C7 middle finger, C8 little finger; T4 nipple level and T10 navel. Treat these as approximate landmarks.
Clinical correlation
Shingles often follows one or two neighboring dermatomes and usually stays on one side of the midline. It is not strictly confined in every case. Root compression can also cause sensory changes, but the pattern need not exactly match a textbook map.
Frequently asked questions
What are the roots of the dermatomes?
Maps usually begin at C2 and continue through the sacral and coccygeal levels; C1 has no usual discrete skin territory.
What muscles do the dermatomes supply?
Dermatomes describe sensation, while myotomes describe segmental muscle function. Common reflex associations include biceps/brachioradialis C5–C6, triceps mainly C7, patellar L2–L4 and Achilles mainly S1.
What is the sensory distribution of the dermatomes?
Approximate reference sites include C6 thumb, C7 middle finger, C8 little finger, T4 nipple level, T10 umbilicus, L3 medial knee, L4 medial malleolus, L5 dorsal great-toe region and S1 lateral foot/ankle.
What is the course of the dermatomes?
Cutaneous branches of dorsal and ventral rami reach the skin; limb plexuses redistribute ventral-ramus fibers into named peripheral nerves.