Referred pain results when a nerve is irritated or injured. When this happens, often the entire length of the nerve communicates pain signals to the brain, even though the actual injury site is limited. A common example is sciatica caused by pressure on the sciatic nerve from a low-back injury such as a bulging or herniated disk. Although the injury site is in the lower back, the victim feels pain down the outside of one or both legs, often to the toes. This pain is usually a burning sensation, perhaps accompanied by tingling.
Herniated or bulging disks aren't the only cause of sciatica; sometimes a muscle spasm or excessive tightness in the lower back or buttocks can irritate the sciatic nerve, causing referred pain down a leg. In either case, this type of pain indicates pressure on the nerve, and you should check with your physician. If the pain comes with muscle weakness, loss of feeling, or bowel or bladder problems, it's a sign of a potentially very serious injury and should be looked at right away.
Arthritic changes in the vertebrae of the neck are another common source of referred pain; often the pain is manifested in the arm, or even the hand or fingers.
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