A dermatome is an area of skin which is innervated by a single spinal nerve. There are 30 pairs of dermatomes in the body, from the skull to the toes, and each can be traced back to a specific nerve root. Although most maps of the dermatomes show distinct zones, there is in fact a fair amount of overlap, but understanding how these areas work can be important in the treatment and diagnosis of disease.
Along the torso, the dermatomes look like horizontal bands, with each band corresponding to a particular nerve root. The arms and legs have longitudinal bands, which explains why pain sometimes shoots down an arm or a leg, because it is following the dermatome. Cervical, thoracic, lumbar, and sacral nerves all supply nerve fibers to various dermatomes in the body. For example, the back of the leg is covered by a dermatome which is innervated by the first sacral nerve.
In patients with neurological problems, pain in a particular area can be a very revealing symptom. A doctor can study the pain to figure out which dermatome it is confined to, and use this information to look for signs of damage in a particular area. For example, someone with spinal compression causing a pinched nerve might experience significant pain in the dermatome innervated by that nerve. Likewise, in someone with a shingles outbreak, the areas of pain on the body would correspond with particular spinal nerves affected by the virus which causes shingles.
Pain in a dermatome is a symptom, not a condition, but it can be a very important symptom. Patients who report chronic pain or transient pain in a particular zone of their bodies can be revealing important information about a neurological condition or spinal cord problem, and a doctor can use that information to recommend treatment or refer the patient to a specialist who can address the problem.
This type of pain can be extremely frustrating for patients, because it has no clear physical cause, and it can come and go sporadically, depending on the type of damage. The skin may feel like it is itching, burning, or experiencing other sensations which are not really occurring, including extreme cold or severe pain. By tracing the pain back to the responsible nerve, a doctor can develop a treatment plan to address or manage the underlying cause so that the patient will not experience the undesirable sensations associated with nerve damage or other impairments to nerve function.