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MRI testing
Magnetic Resonance Imaging (MRI) allows unparalleled views of soft tissues within the body. Changes that include water content of tissues, swelling or changes of soft tissue structures, such as a lumbar disk, can be measured in millimeters. Sometimes, it is so sensitive that we get more information than we can use.
Abnormal MRI may just be consistent with aging
Many times the MRI is called abnormal even though some of the issues may be only those consistent with aging. Spinal aging shows up as degenerative disk disease. This includes disk space narrowing, disk dehydration, vertebral bone spurs, annular tears (a tear in the outer rim of the disk) and disk bulging as well as herniation. Past age 30, 30 to 40 percent of the population has a disk herniation even though they have never had low back pain. This means that degenerative disk changes frequently have nothing to do with low back pain.
Remember that in more than 90 percent of low back pain cases, there is no absolute diagnosis possible. This is true despite the fact that over 50 percent of the time there is some abnormality read on an MRI. This can become a problem if it leads you or your doctor to consider more aggressive treatments, such as surgery where in fact it is not necessary.
MRI is helpful when
Pain radiatesOne of the difficulties with low back pain is that only a small percentage of the disk herniations picked up on MRI screening are shown to cause the pain. This happens when the MRI shows a disk herniation that puts pressure on one of the nerves as it exits the spine. When this happens, a person tends to have pain radiating below the knee, frequently associated with numbness and tingling and sometimes loss of sensation or strength. These radiating symptoms are the strongest reason to get an MRI. Without these symptoms, the test is not only expensive, but may confuse the picture and delay treatment.
Pain is persistentIf pain lasts more than six weeks, especially if it is felt that stenosis (narrowing of the spinal canal), infection, fracture or tumor may be causing the pain, an MRI may be useful.
Timing of MRI
Usually this test will not be ordered before six weeks unless symptoms of radiating pain, numbness or weakness have not improved or have worsened. Testing has no place in the early treatment of low back pain if these more severe symptoms are not present.
Below are only a few of the studies which support the above.
Jenson MC, et al. Magnetic Resonance Imaging of the lumbar spine in people without back pain. New Engl J Med 1994; 331(2): 69-73.
Boden SD, et al. Abnormal magnetic resonance scans in asymptomatic subjects: a prospective investigation. J Bone Joint Surg Am 1990; 72(3): 403-408.
Stadnik TW, et al. Annular tears and disk herniation in the absence of low back pain or sciatica. Radiology, Jan 1998, 206(1): 49-55.
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