Dermatom

A dermatome, sometimes called a dermatom, is the area of skin innervated by sensory fibers from a single spinal nerve root. The concept is used in anatomy and neurology to describe the distribution of sensation on the body surface and to localize neurological lesions.

In humans there are 31 spinal nerves: eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal. Each nerve carries sensory fibers that innervate a specific skin region. Dermatomes on the trunk form band-like stripes, while those of the limbs run longitudinally. There is often overlap between adjacent dermatomes, so loss of sensation in a single dermatome is not always complete.

Developmentally, dermatomes arise from the dermatome portion of somites during embryogenesis. The somite differentiates into the dermatome (dorsal dermis), myotome (muscles), and sclerotome (vertebrae and related structures). The adult pattern reflects this segmented origin, though individual variability and anatomical overlap exist.

Clinically, dermatomes are used to localize nervous system pathology. Reactivation of varicella-zoster virus (herpes zoster) typically produces a painful, vesicular rash in a dermatomal distribution. Dermatomal testing helps assess sensory loss or nerve-root level in radiculopathy, spinal cord injury, or anesthesia planning.

See also: dermatome map, myotome, somite, shingles, radiculopathy.