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When is Imaging Helpful for Patients with Back Pain?
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Since
the lifetime prevalence of low back pain is about eighty percent, it is
hardly surprising that back pain is one the most common reasons for
patients to seek medical care. However, in the vast majority of cases,
acute back pain (duration less than three months) is a self-limited
condition that resolves with analgesic treatment and activity
modification. In more than 80% of cases of back pain (Table 1)
imaging will not affect treatment. However, it may lead to unnecessary
additional testing due to the discovery of incidental benign lesions
and nonspecific degenerative processes that may also occur in
asymptomatic individuals.
In a recent study of
patients with low back pain who had been referred for radiographic
evaluation, only 3.7% went on to have surgery. However, the rate of
surgeries performed on those who had been randomly assigned to MRI was
double that of those who were assessed with plain film radiography.
Furthermore, there was no difference in the outcome (functional
disability and pain) in these two groups.
Nevertheless, low back pain will sometimes reflect a more serious condition than uncomplicated lumbar |
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Figures A and B:
In a 72 year old patient with intermittent low back pain, MR images of
the lumber spine show multi-level abnormalities, such as severe spinal
stenosis at L3-4 and disk herniation at L5-S1, that are far more
impressive than the degree of symptoms.
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strain
or sprain. The challenge is to identify red flags that would
distinguish patients who should have a more intensive work-up. The
American College of Radiology has put substantial effort into the
development of criteria that may justify further evaluation of patients
with imaging (Table 2).
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Table 1. Pretest Probability of Disorders that Cause Low Back Pain
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| Lumbar strain or sprain |
70%
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| Degenerative processes |
10%
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| Herniated disc |
4%
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| Osteoporotic compression fracture |
4%
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| Spinal stenosis |
3%
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| Spondylolisthesis |
2%
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| Traumatic fracture |
<1%
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| Ankylosing spondylitis |
0.3%
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| Metastatic cancer |
0.7%
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| Spinal infections |
0.1%
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Non-spinal causes
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2%
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Table 2. Indications for Further Evaluation by Imaging*
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Recent significant trauma
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Unexplained weight loss
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Unexplained fever
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Immunosuppression
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History of Cancer
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IV drug use
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Prolonged use of corticosteroids
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Osteoporosis
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Age > 70
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Duration longer than 3 months
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*From American College of Radiology Criteria
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Imaging Modalities for the Spine
Conventional
radiography may be sufficient as a screening tool in the setting of
trauma, prolonged steroid use, and osteoporosis in elderly patients
because it can show vertebral compression fractures. Other imaging
modalities may be warranted in the setting of suspected malignancy or
infection, even if plain radiographs are negative. In patients with low
back pain, the most common clinical indications for advanced imaging
include radiating pain (radiculopathy, sciatica) or symptoms of nerve
root compression due to cauda equina syndrome (bilateral leg weakness,
urinary retention and saddle anesthesia), often reflecting disc
herniation and/or spinal stenosis.
Although the
appropriate selection of imaging modality can be challenging, MRI is
usually the modality of choice. MRI is superior to CT for the depiction
of disc abnormalities and bone marrow lesions, although CT can improve
the assessment of cortical bone and, therefore, better delineate some
fractures. MRI with or without contrast (gadolinium) enhancement
reliably demonstrates vertebral infections and malignancy. MRI has
taken over the role of isotope bone scan in the spine, but the bone
scan remains important when a survey of the entire skeleton is
necessary.
If MRI is contraindicated, isotope bone scan and/or CT may be substituted when there is a suspicion of
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infection
or malignancy. In the case of radiating pain or cauda equina syndrome,
CT myelography is effective but requires lumbar puncture for the
injection of iodinated contrast. When other studies fail to localize
the source of pain, image-guided injections, such as nerve root block
or facet block, may have diagnostic value.
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Figures C and D:
In a 52 year old patient with known lung carcinoma, MR images show two
focal lesions (L1 and L4) that enhance densely after contrast
administration. Radiographs were normal in appearance. Back
pain was the first indication of metastatic disease.
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Scheduling
If
emergency imaging for back pain is warranted, the patient should be
sent to the Emergency Department at MGH, where radiography, MRI, or CT
will be performed. In other cases, imaging can be performed at
MassGeneralWest in Waltham, Mass General Imaging in Chelsea or the main
MGH campus. It can be ordered online via the Radiology Order Entry
(ROE) System (http://mghroe
) or by calling 4-XRAY (617-724-9729). Results
are made available to physicians online within 24-48 hours.
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Further Information
For
further questions on imaging for back pain and image-guided treatments
(e.g. steroid injections, vertebroplasty), please contact Dr. William Palmer, MGH Department of Radiology, at 617-726-7719 or visit www.mghbackpain.org.
For general information regarding MGH Radiology services and locations, please contact Kristen Dean at 617-724-4902.
This article provided useful information about the appropriate use of imaging studies:
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References
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Expert Panel on Neurologic Imaging: Anderson, RE, Drayer, BP; Braffman, B, et al. (2000) American College Of Radiology Appropriateness Criteria: Acute low back pain - radiculopathy. (Download pdf)
Borenstein, DG, O'Mara, JW, Jr., Boden, SD, Lauerman, WC, et al. (2001) The
value of magnetic resonance imaging of the lumbar spine to predict
low-back pain in asymptomatic subjects : a seven-year follow-up study. J Bone Joint Surg Am 83-A: 1306-11
Jarvik, JG and Deyo, RA.(2002) Diagnostic evaluation of low back pain with emphasis on imaging. Ann Intern Med 137: 586-97
Jarvik, JG, Hollingworth, W, Martin, B, Emerson, SS, et al. (2003) Rapid magnetic resonance imaging vs radiographs for patients with low back pain: a randomized controlled trial. JAMA 289: 2810-8
Jensen, MC, Brant-Zawadzki, MN, Obuchowski, N, Modic, MT, et al. (1994) Magnetic resonance imaging of the lumbar spine in people without back pain. N Engl J Med 331: 69-73
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