The C5 dermatome in the upper limb corresponds to which anatomical region?

Explanation

## C5 Dermatome Distribution in the Upper Limb **Key Point:** The **C5 dermatome** covers the **lateral arm and the lateral (thumb) side of the forearm**, extending to the thumb and lateral hand. This is the most proximal cervical dermatome of the upper limb. ### Upper Limb Dermatome Map **High-Yield:** Understanding cervical dermatomes is essential for diagnosing nerve root lesions and cervical myelopathy: | Dermatome | Region | | --- | --- | | C4 | Shoulder tip (acromion) | | **C5** | **Lateral arm, lateral forearm, thumb side** | | C6 | Lateral forearm, thumb, index finger | | C7 | Middle and ring fingers, dorsal hand | | C8 | Medial forearm, little finger, medial hand | | T1 | Medial arm (axilla to elbow) | ### Clinical Correlation **Clinical Pearl:** C5 root lesions (e.g., C5 radiculopathy, cervical myelopathy at C5 level) present with sensory loss over the **lateral shoulder and lateral forearm**. This is tested by examining sensation over the lateral arm and thumb. **Mnemonic:** **"C5 = Lateral (thumb) side"** — Remember that C5 is the most lateral cervical dermatome in the upper limb, covering the thumb-side structures. ### Clinical Applications - **C5 radiculopathy:** Sensory loss on lateral arm; weakness of shoulder abduction (axillary nerve, C5–C6) - **C5 myelopathy:** Bilateral C5 dermatome sensory loss; upper motor neuron signs below the level - **Brachial plexus injury (C5 root avulsion):** Loss of sensation in C5 territory; Horner syndrome may occur if sympathetic fibers are involved [cite:Clinically Oriented Anatomy 8e Ch 6; Inderbir Singh's Anatomy 13e Ch 3]