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Imaging - in Asymptomatic Subjects 
  Literature Reviewed.  Six articles were found that evaluated lumbar spinal imaging findings in "asymptomatic" subjects with no low back symptoms.  These studies included one evaluating CT scan,275 four on MRI,273, 291,322, 323 and one for plain myelography.274  Other articles contained information used by the panel, but did not meet article selection criteria.30, 40, 49, 50 
  Evidence on Efficacy.  Boden, Wiesel, Tsourmas, Feffer, et al.275 evaluated readings of CT scans for 52 subjects with no history of low back problems, with all scans read independently by three neuroradiologists blinded to other data.  For those under age 40, herniated discs were diagnosed in an average of 19.5 percent of subjects (range for the three readers, 13 to 24 percent).  For subjects over age 40, those who had abnormal findings averaged 50 percent (with a range of 30 to 82 percent among the readers). Included were 27 percent of subjects diagnosed with herniated discs, 10 percent with facet joint hypertrophy, and 3 percent with spinal stenosis. Technical quality of this study was considered adequate. 
  Boden, Davis, Dina, et al.273 evaluated readings of MRI scans in 67 subjects with no history of back problems.  Scans were read by three neuroradiologists blinded to all other data after the scans were randomly mixed with scans of symptomatic patients who had proven back pathology.  Of the asymptomatic subjects, 35 were age 20 to 39, 18 were age 40 to 59, and 14 were age 60 and over.  The percentages for each of the above age groups were reported respectively by neuroradiologists as: a definite or probable abnormality in 22 percent, 22 percent, and 57 percent; bulging disc in 56 percent, 50 percent, and 79 percent; disc herniation in 21 percent, 22 percent, and 36 percent; degenerative disc in 34 percent, 59 percent, and 93 percent; spinal stenosis in 1 percent, 0 percent, and 21 percent.  This study was considered of good technical quality. Jensen '94, Borenstein '01, Jarvik '01 show similar trends.273a-c  Of more than 20 studies of lumbar spine imaging age-related changes begin to occur in the second decade of life, and by age 50, “degenerative” changes are “the rule, not the exception.” The majority of people over the age of forty have evidence of what is termed disc degeneration, disc herniation or other aging changes in the spine. (See Radiographic Diagnosis) (See also Boden et al,`90 and Masumoto et al.`98 in Neck Imaging)  
Kappa Delta Award winning Identical twins studies by Battie Videman 274e-g found degenerative changes are dominated by genetics with little influence from life exposures short of an event causing obvious fracture or dislocation.  When controlling for wide individual variations by using identical twin, varied exposures to work, spinal load, activity and vibration (6 fold differences) have very modest impact on development of MRI lumbar spine degenerative changes while genetics expression remain extremely similar.Only smoking seems to speed aging of the lower spine as the overwhelming influences on what we see on MRI are genetic factors. 
  Paajanen, Erkintalo, Dahlström, et al.291 evaluated MRI scans in age-20 male military conscripts including 75 subjects with low back pain and 34 controls with no history of low back problems.  Five intervertebral discs, from L1-L2 to L5-S1, were evaluated for each subject.  Disc degeneration, indicated by reduced MRI signal intensity for the disc, was found in 57 percent of patients with low back problems and 35 percent of controls.  The authors stated that it was unclear if the positive findings in controls represented pathological processes or merely normal aging changes that did not predispose to future low back problems.  The technical quality of the MRI scans in this study was considered suboptimal because low field strength MRI (0.02 T) was used. 
  Powell, Wilson, Szypryt, et al.322 evaluated the MRI scans in 302 women who had no symptoms of low back problems, but who had the scans done for nonback obstetrical problems.  Using reduced MRI signal intensity of the disc as an indication of disc degeneration, the authors found one or more degenerative discs in 34 percent of women age 21 to 30, in 60 percent of women age 31 to 40, and in 95 percent of women by age 70.  Bulging discs were found on MRI in 11 percent of 82 pregnant women and 13 percent of 56 women who had never been pregnant (these data not presented by age group). 
  Weinreb, Wolbarsht, Cohen, et al.323 evaluated MRI findings in 45 pregnant women age 20 to 39 and in 41 nonpregnant women age 19 to 40 with no current low back symptoms.  Three intervertebral disc levels, L3-L4, L4-L5, and L5-S1, were evaluated for all subjects.  No significant differences were found between pregnant and nonpregnant women in terms of the percentage with lumbar disc herniation (9 percent compared with 10 percent) or disc bulging without herniation (44 percent in each group). The technical quality of this study was considered suboptimal because testing protocols varied between subjects and low field strength MRI (0.35 T) was used. 
  Hitselberger and Witten274 reviewed lumbar myelograms done in 300 patients with no prior history of radiculopathy.  The technical quality of this study was considered poor because oil-based contrast media were used, which are less sensitive than more modern techniques.  Still, 24 percent had myelographic evidence of lumbar disc herniation, 9.3 percent had spinal stenosis without a history of radicular symptoms (1 of 300 with a complete block of the dye).  This study was of limited value because findings were not given by specific age groups, and the age range of subjects was 18 to 76 with a mean age of 51. 
  Degenerative discs, bulging discs, and even herniated discs are part of the aging process for the spine and may be irrelevant findings; they are seen on imaging tests of the lumbar spine in a significant percentage of subjects with no history of low back problems.  Therefore, abnormal imaging findings seen in a patient with low back problems may or may not be related to that individual's symptoms.  A herniated disc noted on an imaging test is more likely to be associated with a clinically significant nerve root compromise in patients when there are other findings (such as leg pain, positive straight leg raising, neurologic deficits, or a positive electrodiagnostic test) that suggest physiologic nerve root compromise.30, 40, 49, 50 
  Potential Harms and Costs.  Factors that may influence the decision on which imaging test to use in diagnosing low back problems include the following: (1) tissue of greatest interest for imaging (CT better for bone, MRI better for imaging neural tissues and bone marrow and for diagnosing tumor or infection); (2) claustrophobia (more of a problem for MRI); (3) obesity (both CT and MRI scanners have a maximum table weight, so that extremely heavy patients may need to have myelography); (4) presence of internal metallic objects such as implanted medical devices, metallic surgical clips, or metallic objects or fragments in the eye, which can be a major problem for MRI (and sometimes for CT); (5) preference of the consultant and of the patient; (6) availability, cost, and potential side effects of the test. 
  CT-myelography and myelography have a higher risk of complications than CT or MRI (for example, post-spinal-tap headaches and adverse reactions to contrast media).  For CT scan, potential harms include minimal x-ray exposure (including gonadal radiation exposure in females).  Amount of exposure (less than two rads) is similar to that from two standard x-ray views of the lumbar spine.  For MRI scan, there have been no clearly documented adverse health effects.  Long-term effects of magnetic field exposure from MRI are unknown, but this test is generally believed to involve minimal risk.  CT scan, MRI scan, CT-myelography, and plain myelography are all considered moderate to expensive in cost. 
  Summary of Findings.  Given the benign natural history of low back problems, with 80 to 90 percent of patients expected to improve at 1 month even without treatment, routine spinal imaging tests are not generally necessary during the first month of symptoms except when a red flag (suggesting a medically emergent condition) is noted on medical history and physical examination.  After 1 month of symptoms, the use of imaging tests may be appropriate when surgery is being considered for a specific detectable loss of neurologic function or to further evaluate possibly serious spinal pathology in the presence of Red Flags. Imaging should be suggested to the patient as a means of seeking serious problems not to find the rarely detecable cause of usually fleeting back pain. 
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