Along the thorax and abdomen the dermatomes are like a stack of discs forming a human, each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different: the dermatomes run longitudinally along the limbs. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints.
Referred pain: Conscious perception of visceral sensations map to specific regions of the body, as shown in this chart. Some sensations are felt locally, whereas others are perceived as affecting areas that are quite distant from the involved organ.
A dermatome is an area of skin supplied by sensory neurons that arise from a spinal nerve ganglion. Symptoms that follow a dermatome (e.g. like pain or a rash) may indicate a pathology that involves the related nerve root. Examples include somatic dysfunction of the spine or viral infection. Referred pain usually involves a specific, "referred" location so is not associated with a dermatome.
Viruses that lie dormant in nerve ganglia (e.g. varicella zoster virus, which causes both chickenpox and herpes zoster commonly shingles), often cause either pain, rash or both in a pattern defined by a dermatome. However, the symptoms may not appear across the entire dermatome.
Important dermatomes and anatomical landmarks
Following is a list of spinal nerves and points that are characteristically belonging to the dermatome of each nerve:
Dermatomes of the Lower Limb (Modified, from Fender, after Foerster)