Howard shuffles slowly into his physician's office, complaining of persistent pain in his right foot. An examination reveals that his foot is fine, but that he has a pinched nerve in his neck and that's what is making his foot hurt.
Meanwhile, a few blocks down the street, Mary Ann limps into her doctor's examining room, almost in tears over the relentless ache in her left knee. It turns out that both of her knees are in perfect shape. The doctor, however, informs her that the pain in her knee might be a sign of a hip disorder, and subsequent examination confirms this to be the case.
What both patients are experiencing is a phenomenon known as "referred pain," which Daniel Mazanec, M.D., a rheumatologist and director of the Spine Center at Cleveland Clinic, describes simply as "pain in an area of the body that is distant from the source of the pain," according to the Cleveland Clinic's Arthritis Advisor. A classic example of referred pain, he notes, is the distress experienced in the left arm by a person in the midst of a heart attack. And for some people with acute appendicitis, the first warning sign will not be in the abdomen but in the right shoulder.
Referred pain is not to be confused with radiated pain. "If you have a herniated disk," Dr. Mazanec explains, "you'll have pain in your back and you're also likely to have it in your leg, because that's where the nerve that's irritated happens to travel and the pain can be expected to radiate along that pathway. Referred pain, on the other hand, travels along unexpected pathways."
Shared 'wiring' systemIn describing the complex neurologic processes that are associated with referred pain, Dr. Mazanec says, "Think of innervation the nervous system that serves a muscle or an organ as an interconnected wiring network that travels throughout the body. A liver abscess can result in shoulder pain, for example, because the liver is situated below the diaphragm, and the 'wires' (nerves) from the diaphragm enter the spinal cord at the same point as the wires (nerves) from the shoulder. They share the same neurologic pathways to the brain, and sometimes the electrical signals become intermingled."
This intermingling of pathways is not an abnormality, he notes. Rather, it results from the normal emergence of the nervous system in the embryonic stage, when the development of all of the body's "wiring" proceeds in close proximity. "Over time," says Dr. Mazanec, "the pathways serve different parts of the body, but they continue to share the innervation they shared in the embryo, when they were geographically in the same location."
Arthritic painPatients with arthritis can also experience referred pain. "It almost always occurs in the joints," says Dr. Mazanec, "and it is most frequently observed in people with hip osteoarthritis. It's not unusual for patients with this condition to experience pain in the groin. But there may also be discomfort or pain in the front of the thigh that runs all the way down to the knee."
Knee pain that accompanies hip osteoarthritis may intensify over time, Dr. Mazanec explains, and worsening discomfort will result from movement of the hip rather than from overuse of the knee, since the hip-to-knee referral of pain does not go both ways.
Another example of referred pain would be evident in a patient with cervical (neck) arthritis. "In this case," says Dr. Mazanec, "you can experience what we call nerve entrapment, and the pain caused by the pinched nerve can radiate down the arm. But if you have an arthritic problem in the joints of the neck and there is no nerve entrapment, that pain can be perceived in the upper back."
If a patient complains of persistent knee pain, it is by no means assumed that the hip is responsible for the problem, since knee osteoarthritis is common. "We would examine the knee," says Dr. Mazanec, "but we would also look at the hip. If we conclude that the knee joint is normal, we would assess the patient's mobility. We might then suspect that hip osteoarthritis is the source of the knee pain.
"We wouldn't immediately conclude that it's a case of referred pain from the hip," says Dr. Mazanec. "We would confirm our diagnosis with an X-ray." In some cases, he adds, the examination may yield "confusing" results, in which case the patient might be given a hip-joint injection of a novocaine-like drug. "If this eliminates the knee pain," says Dr. Mazanec, "it would confirm that the problem is in the hip."
Treatment optionsIf knee pain is found to have its source in an arthritic hip, therapy would center primarily on treatment of the hip, ranging from the use of nonsteroidal anti-inflammatory drugs, to physical therapy, to hip replacement.
Dr. Mazanec points out that referred pain is not an imaginary phenomenon. It is real and may signal the presence of a serious underlying condition affecting a remote part of the body. "If you experience any kind of pain," he advises, "don't wait a month to see if it goes away. If it persists, see your doctor."
What You Can DoKeep track of your pain's characteristics and communicate this information to your physician. If the site of your pain appears normal, have an X-ray of other body components that may be causing the pain.
Talk to your doctor about treatment options drug therapy, physical therapy, or replacement.