Conducting and Interpreting DiscographyDiscography to test for painful discs doesn't always work. Sometimes there are false-positives leading to unnecessary surgery. A false-positive means the patient's test suggests a painful disc when there's nothing wrong with that disc. Discography is done by injecting a dye into the disc. Damaged discs are chemically sensitive and react to the dye. The test causes back pain right away.
In this study researchers check to see if using low-pressure as a positive test would reduce the number of false-positives. When pain was caused by pressure less than 22 psi, the test was considered positive.
The results from discography in two groups were compared using this definition of a positive test. One group didn't have low back pain (LBP). This group included people with no pain, other types of chronic pain, and previous back pain. The second group had persistent back pain and was considering surgery. Everyone in both groups was also given psychologic tests to assess levels of distress and depression.
The authors report about 25 percent of the subjects currently without back pain had a positive discography at 22 psi. By studying the group closely they found three subgroups most likely to have these results. They included subjects with abnormal psychologic tests, people with chronic pain problems, and those with true disc damage but no back pain. Only the subjects with no LBP, no history of LBP, and no chronic pain had no pain with low-pressure injection.
The authors conclude that using a low-pressure psi as a positive discography won't eliminate false-positive tests. There are too many other factors responsible for a painful response to low-pressure discography. Newer and better diagnostic tests are needed.
Eugene J. Carragee, MD, et al. Low-Pressure Positive Discography in Subjects Asymptomatic of Significant Low Back Pain Illness. In Spine. March 1, 2006. Vol. 31. No. 5. Pp. 505-509.
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