The T3 dermatome is a band of skin wrapping around the chest from the spine to the front midline at about the level of the third intercostal space. It sits just below the T2 band and forms a horizontal strip around the trunk. Its skin is supplied by the cutaneous branches of the third intercostal nerve.
| Nerve root | T3 |
|---|---|
| Area | Band around the chest at about the third intercostal space |
| How to test | Light touch and pinprick are compared side to side at the ISNCSCI key sensory point: in the midclavicular line at the third intercostal space. |
| Nerve Supply | Third intercostal nerve (lateral and anterior cutaneous branches); Posterior rami of thoracic spinal nerves |
Carries touch, pain and temperature sensation from this strip of skin to the spinal cord through the T3 dorsal root.
Thoracic dermatomes are best known from shingles, which produces a one-sided painful rash that stops at the midline. Thoracic disc herniations are rare, so a sensory level on the chest should raise concern for spinal cord compression by tumour, infection or a disc. Dermatome maps differ between sources (Foerster, Keegan and Garrett, and modern evidence-based maps disagree), and neighbouring dermatomes overlap, so borders are approximate.
Reactivated varicella zoster virus in the T3 dorsal root ganglion causes a painful band of blistering rash confined to this dermatome, sometimes followed by postherpetic neuralgia.
Compression of the cord at or above this level from tumour, abscess or disc can produce a sensory level on the chest with leg weakness.
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