Dermatome Testing: Clinical Utility in Neurological Diagnosis

Dermatomal sensory testing maps sensory deficits to specific spinal nerve roots, providing topographic localization of neurological lesions.

Clinical Applications

1. Spinal Cord Injury Level: Sensory level = lowest normal dermatome. All below impaired. Critical for ASIA impairment scale.
2. Radiculopathy (Nerve Root Compression): Dermatomal pain/numbness/tingling localizes root (e.g., C6 thumb/index, L5 dorsum foot, S1 lateral foot). Differentiates from peripheral neuropathy (stocking-glove) or plexopathy.
3. Peripheral Neuropathy Pattern Recognition: Length-dependent (distal symmetric) vs. mononeuropathy multiplex vs. radiculopathy.
4. Treatment Monitoring: Serial exams track recovery (e.g., post-decompression, immunotherapy for CIDP).
5. Functional Prognostication: Sensory loss predicts ADL limitations, fall risk, wound healing.

Testing Technique

• Light touch (cotton wisp), pinprick (sharp/dull), temperature (tuning fork cold), vibration (128 Hz), proprioception (joint position).
• Compare sides; test key dermatomes (C5-T1, L2-S2).
• Map boundaries of abnormality.

Key Dermatomes (Quick Reference)

• C4: Acromioclavicular joint.
• C5: Lateral arm.
• C6: Thumb, radial forearm.
• C7: Middle finger.
• C8: Little finger, ulnar forearm.
• T4: Nipple line.
• T10: Umbilicus.
• L1: Inguinal ligament.
• L4: Medial malleolus.
• L5: Dorsum foot, great toe.
• S1: Lateral foot, little toe.
• S2-S5: Perineum, anogenital.

Dermatomal testing is a cornerstone of the neurological exam.