Dermatomal

Dermatomal refers to a dermatome, which is the area of skin innervated by sensory fibers from a single spinal nerve root. Each spinal nerve contains dorsal (sensory) and ventral (motor) components, and the sensory input from a dorsal root supplies a distinct, though overlapping, skin region. The term is used for clinical localization of sensory loss or pain to a specific nerve root level. The face is an exception, as its sensory innervation is provided by the trigeminal nerve, not spinal dermatomes.

Anatomy and mapping of dermatomes are approximate. Dermatome maps show the typical boundaries of sensory innervation for each nerve root, from the cervical through the sacral levels (e.g., C2 to C8, T1–T12, L1–L5, S1–S5). However, there is substantial natural overlap between adjacent dermatomes, and individual variation is common. Therefore, sharp, complete loss of sensation in a dermatome is less common than partial loss, and precise localization may require multiple sensory modalities and clinical correlation.

Clinical relevance includes diagnosing radiculopathy, where pain, numbness, or weakness follows a dermatomal pattern, and identifying the distribution of herpes zoster (shingles), which characteristically presents as a painful, vesicular rash in a dermatomal distribution corresponding to reactivated varicella-zoster virus. Dermatomal assessment remains a fundamental component of neurologic examination and localization.