Dermatomes | Dermatome

Dermatomes are areas of the skin supplied with nerve fibers by a single nerve root. There are 8 nerve roots for the 7 cervical vertebrae; otherwise, each of the 12 thoracic, 5 lumbar, and 5 sacral vertebrae has a single nerve root that supplies specific areas of the skin. These dermatomes allow us the ability to map out the entire body, and to use nerve evaluation tests on the skin to determine which nerve roots are affected by compression or some other types of structural changes that affects the nerve's ability to send signals. Tests such as the lower body nerve evaluation, conducted by doctors, are imperfect, because they may not indicate an exact location of the nerve impingement, and they don't indicate the cause of the compression. Nevertheless, these types of nerve tests that measure the sensitivity of dermatomes can help patients determine a diagnosis to the cause of upper back pain or lower back pain.



To get a better picture of what the dermatome map of the body looks like, take a look at the following diagram. Schematic demarcation of dermatomes are shown as distinct segments. Note, there actually aren't perfect boundaries between one dermatome to another, as shown in the graphic here. There is actually considerable overlap between any two adjacent dermatomes.

The facts known about dermatomes and as presented in this diagram will help doctors towards a diagnosis as the perform tests such as the lower body nerve evaluation. In this test, the doctor runs a device called a pinwheel along the skin, from the hips to the feet. The doctor, while performing this part of the exam, will receive feedback from the patient if any changes in sensitivity are noticed while the wheel is run over a particular section (less feeling, or a heightened sensitivity). For example, if a patient presents in the clinic with weakness/burning/tingling on one foot, the doctor may suggest lumbar nerve root compression, but the nerve evaluation test may be able to provide more information. Changes in sensation on the outside of the foot indicate nerve root damage at the level of S1. Loss of sensitivity in the front middle of the foot indicates L5 nerve root compression. Loss of or diminished feeling in the side of the foot indicate nerve root compression at the level of L4. Loss of sensation in the back middle of the foot also indicate nerve root compression at the level of L5, as seen in the picture.

Clinical significance and Limitations. Dermatome mapping an examination are useful in back pain medicine in finding the individual nerve root being compressed. The two limitations are that it does not provide the exact site of nerve root compression (that may be confirmed by MRI or CT scan), nor the cause of the nerve damage. The tests, using dermatome mapping, may indicate the nerve root involved but not necessarily the location along the path of the nerve. Other tests to measure nerve root function or dysfunction include the myelogram, also known as EMG.

Treatment: Treatment for nerve root disorders depend on the length of time of symptom suffering, severity of symptoms, and the cause of the problem. Generally, treatments may become less conservative and more invasive (e.g. surgery) after conservative treatments have been tried and failed to produce results. Treatments may include analgesics, physical therapy, and disk removal for bulging discs and ruptured discs.