Dermatome

A dermatome is an area of skin receiving sensory innervation from a single spinal root (one segment of the spinal cord). Each such segment (except for the first cervical segment, C1) corresponds to a specific area on the surface of the body.

All body dermatomes form a kind of innervation map, which is used in neurology to determine the level of damage to the spinal cord or spinal roots. Neighboring dermatomes partially overlap ensuring reliability of the sensory system.

Anatomy and Physiology

Each spinal nerve exits the vertebral canal and carries sensory (afferent) fibers from a specific area of the skin. These fibers transmit information about touch, pain, temperature, and pressure to the central nervous system.

The set of these fibers stemming from a single root and the area they innervate are called a dermatome. For example, the L5 nerve root innervates the skin on the anterior region of the leg and the dorsum of the foot.

Clinical Significance

The dermatome map is a fundamental tool in the topical diagnosis of neurological diseases. Symptoms (pain, numbness, tingling, skin rash) that clearly correspond to the boundaries of one or more dermatomes are very likely to indicate damage to the corresponding nerve root.

Clinical examples:

• Radiculopathy. Compression or inflammation of the spinal root (e.g., in a herniated disc) causes pain and sensory disturbance exactly in the area of the corresponding dermatome. Sciatica is a classic example.
• Herpes zoster (shingles). Chickenpox virus (Varicella zoster) remains dormant in the nerve ganglia and, when reactivated, causes a characteristic painful rash that spreads precisely along the course of a single dermatome.

Assessing sensitivity in different dermatomes is an important part of a neurological examination, allowing a doctor to determine the extent of damage to the nervous system.