liminfoDermatome Map
Free reference guide: Dermatome Map
About Dermatome Map
The Dermatome Map Reference is a detailed clinical guide covering all major spinal nerve root sensory distributions from C2 through S5, organized into cervical (C2-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5), and clinical testing categories. Each entry includes the specific cutaneous territory, responsible nerve, associated muscles, relevant reflexes, recommended sensory testing sites, and clinical significance for diagnosing radiculopathy and spinal cord injuries.
Key anatomical landmarks are prominently featured: C5 at the regimental badge area (deltoid), C6 at the dorsal thumb, C7 at the middle finger, T4 at the nipple line, T6 at the xiphoid process, T10 at the umbilicus, L4 at the medial malleolus, L5 at the 1st-2nd toe web space, and S1 at the lateral foot. These landmarks are essential for rapid neurological level assessment in spinal cord injury, epidural anesthesia verification, and emergency triage.
The clinical testing section provides standardized sensory examination protocols, complete radiculopathy pattern summaries (sensory, motor, and reflex findings for C5, C6, C7, L4, L5, S1), peripheral nerve versus dermatome differentiation criteria, and common neuropathy patterns including carpal tunnel syndrome, ulnar nerve entrapment, peroneal nerve palsy, piriformis syndrome, and diabetic polyneuropathy with their characteristic distribution patterns.
Key Features
- Complete C2-S5 dermatome entries with cutaneous territory, nerve supply, muscle associations, reflexes, and clinical correlations
- Key landmark reference: T4 nipple line, T6 xiphoid, T10 umbilicus, L4 medial malleolus, L5 first web space, S1 lateral foot
- Radiculopathy pattern table summarizing sensory deficit, motor weakness, and reflex changes for C5, C6, C7, L4, L5, and S1
- Cauda equina syndrome warning signs: saddle anesthesia (S3-S5), urinary retention, decreased anal tone with 48-hour surgical urgency
- Standard sensory examination protocols for light touch, pinprick, temperature, and vibration testing with bilateral comparison principles
- Peripheral nerve vs dermatome differentiation with carpal tunnel, ulnar entrapment, and peroneal palsy distribution examples
- Thoracic dermatome clinical correlations including autonomic dysreflexia risk above T4 and Beevor sign for T10 lesions
- Common neuropathy patterns: carpal tunnel, ulnar entrapment, peroneal palsy, piriformis syndrome, and diabetic stocking-glove polyneuropathy
Frequently Asked Questions
What spinal nerve levels does this dermatome reference cover?
The reference covers cervical C2 through C8 (7 entries with detailed upper limb distributions), thoracic T1, T4, T6, T10, and T12 (key trunk landmarks), lumbar L1 through L5 (5 entries for lower limb), and sacral S1, S2, and S3-S5 (including perineal/saddle area). Each entry specifies the cutaneous territory, nerve, muscles, reflexes, testing sites, and clinical significance.
How does it explain the key dermatome landmarks?
The reference highlights critical landmarks used in clinical practice: C5 regimental badge area (deltoid), C6 dorsal thumb (most reliable test site), C7 middle finger, C8 little finger, T4 nipple line (spinal cord injury level reference), T6 xiphoid process, T10 umbilicus (Beevor sign reference), L4 medial malleolus, L5 first-second toe web space, and S1 lateral foot. These are essential for neurological level assessment.
What are the cauda equina syndrome warning signs described?
The S3-S5 entry describes saddle anesthesia (perineal/perianal numbness), urinary retention or incontinence, and decreased anal tone as the cardinal signs of cauda equina syndrome. It emphasizes that this is a surgical emergency requiring decompression within 48 hours to prevent permanent neurological deficit, mediated through the pudendal nerve (S2-S4) and coccygeal nerve.
How are radiculopathy patterns summarized?
The reference provides a concise pattern table: C5 (deltoid area sensory loss, shoulder abduction weakness, decreased biceps reflex), C6 (thumb numbness, wrist extension weakness, decreased brachioradialis reflex), C7 (middle finger numbness, elbow extension weakness, decreased triceps reflex), L4 (medial leg sensory loss, knee extension weakness, decreased patellar reflex), L5 (foot dorsum numbness, great toe dorsiflexion weakness, no reflex), S1 (lateral sole numbness, ankle plantarflexion weakness, decreased Achilles reflex).
How does it differentiate peripheral nerve from dermatome distributions?
The reference explains that dermatomes follow band-like patterns from single nerve roots with overlap between adjacent segments (seen in radiculopathy and spinal cord lesions), while peripheral nerve distributions follow specific nerve territories with clear boundaries (seen in entrapment and trauma). It provides examples: carpal tunnel syndrome affects the thumb to radial ring finger (mixed C6-C7 via median nerve), while ulnar entrapment affects the ulnar ring finger and little finger (mixed C8-T1).
What sensory examination methods are described?
The reference covers four standard testing modalities: light touch (cotton or soft brush), pinprick (disposable pin with sharp/dull discrimination), temperature (cold tuning fork metal end), and vibration (128 Hz tuning fork on bony prominences). Key principles include bilateral symmetric comparison, distal-to-proximal testing direction, testing from normal to abnormal areas, eyes closed during examination, and minimum two repetitions for confirmation.
What common neuropathies are included?
Five major neuropathies are described: carpal tunnel syndrome (median nerve with thumb-to-ring finger numbness worse at night, thenar atrophy), ulnar nerve entrapment at the elbow (little finger and ulnar ring finger numbness, interosseous atrophy, claw hand), peroneal nerve palsy (foot drop with dorsal foot sensory loss), piriformis syndrome (sciatic nerve compression with L4-S3 distribution), and diabetic polyneuropathy (symmetric stocking-glove pattern with early vibration sense loss).
Is this reference useful for medical students and residents?
Yes, it is designed as a clinical quick-reference for medical students, neurology/neurosurgery residents, physiatrists, and emergency physicians. Each dermatome entry follows a consistent format with territory, nerve, muscles, reflexes, testing sites, and clinical pearls, making it ideal for bedside neurological examination, board exam preparation, and rapid neurological level assessment in trauma settings.