1) Carragee EJ, Tanner CM, Yang B, Brito JL, Truong T. False-positive finding on lumbar discography: reliability of subjective concordance assessment during provocative disc injection. Spine 1999;24(23):2542-2547.

2) Carragee EJ, Tanner CM, Khurana S, Hayward C, Welsh J, Date E, et al. The rates of false-positive lumbar discography in select patients without low back pain. Spine 2000;25(11):1373-1380.

3) Carragee EJ, Chen Y, Tanner CM, Hayward C, Rossi M, Hagle C. Can discography cause long-term back symptoms in previously asymptomatic subjects? Spine 2000;25(14):1803-1808.

Discography has for the past several years been viewed as the Gold Standard in identifying the intervertebral disc as the primary pain generator in patients with low back pain (LBP). This view was based on a number of studies that have demonstrated its ability to both reproduce some patient's LBP as well as show annular disruption at the level of pain. However, the Gold Standard status of discography has recently been questioned by some, particularly Carragee, et al, as can be seen by the studies reviewed here.

The first study looked at 8 patients who were undergoing an iliac graft for surgery that did not involve the thoracolumbar spine. After the graft they performed discograms and asked them if it reproduced their graft pain. They found that 14 of the 24 injected discs produced some pain response. Of these, 5 were reported as different from their graft pain, 7 were similar and 2 were exact. Of the 10 discs that exhibited annular tears, 5 stimulated pain that was similar or exact. By the usual criteria for discography, 4 of the 8 patients would have been classified as positive. They conclude from this that the false positive rate of discography may be higher than previously expected.

The second study looks at 26 subjects, all without history of LBP. Ten were pain free, 10 had chronic neck and arm pain but no LBP and 6 had primary somatization disorders but no LBP. They found that significant positive pain response to discography along with pain related behavior was seen in 10% of the pain free group, 40% of the chronic cervical pain group and 83% of the somatization disorder group. Discs with annular disruption were more likely to be painful on injection, particularly in those with ongoing compensation issues, chronic pain or abnormal psychometric testing. They conclude from this that false positive discograms are common in those with painful conditions unrelated to the lumbar spine and those with abnormal psychological profiles.

Finally, the third study looked at 26 patients without LBP and split them into 3 groups: 10 patients who had had cervical surgery with excellent results (pain free group), 10 patients who had had cervical surgery with poor results (chronic pain group) and 6 patients with a primary somatization disorder. They did lumbar discography on all of them. There were 2 control groups, 6 with chronic LBP who had undergone discography and 6 somatization subjects who did not undergo discography. They followed them for 1 year.

They found that no subject with normal psychometric testing had persistent pain after 1 year, whereas 6 out of 15 subjects (40%) with abnormal psychometric testing had persistent pain. None of the pain-free group, 20% (2 of 10) of the chronic neck pain group and 66% (4 of 6) of the somatization group had persistent LBP that they attributed to the discography after 1 year. Overall, those with somatization disorder had a prevalence of persistent LBP after discography of 60%. Those subjects with occupational disability seemed especially prone top pain after discography (80%). So the presence of somatization and occupational disability significantly predicted persistent pain after discogram.

They state that if the psychological disorder significantly predisposed the somatization patients to persistent pain, then there should at least be a trend in the somatization patients who were not subjected to discography, but had had other investigations, but this was not the case. Conversely, if the discogram caused actual damage to the disc, there should have been persistent pain across all groups.

It could easily be concluded from these studies that we should look at lumbar discogram with a high degree of skepticism - that the procedure probably is not as valuable as was once thought. But before drawing this conclusion, we must consider the nature of discography and the methodology of these studies.

The second study, which used asymptomatic subjects and showed an apparent degree of false positivity can be seen as problematic for those who understand the proper protocol for discography. A positive discogram is defined by fluoroscopic evidence of internal disc disruption along with, not just the production of pain on injection of the disc, but the reproduction of the patient's pain on injection. How can asymptomatic subjects be used, and their discograms be called positive, when they have no pain to reproduce? So it is impossible to determine false positivity in asymptomatic subjects.

The important findings in these studies, however, is that they demonstrate that those with chronic pain and abnormal psychometric profiles, probably because of central sensitization of their nociceptive tracts (see my previous column on this subject), will likely report pain, that may end up being long term, as a result of discography. This, again, is not a reflection of the weakness of the test as much as it is a demonstration of the power of central sensitization to create the illusion within the central nervous system that tissues are pathologically damaged when in reality there is no such damage. This must be kept in mind when interpreting the results of discography, or any test or examination procedure that involves the reproduction of pain. Pain, as we know, is often an elusive entity, as only the patient can fully experience it. It is up to us to detect its significance, in light of the multifactorial nature of its many potential causes.

Dr. Murphy is in private practice in Rhode Island, as the Clinical Director of the Rhode Island Spine Center. He is currently on the Chiropractic Postgraduate Faculty of NYCC, LACC & CMCC.

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