We have learned on this site that some patients may suffer debilitating back pain and/or leg pain (sciatica) yet not have any positive findings on MRI – i.e., there is no disc herniation or any disc abnormality detected. For these unfortunate patients, the diagnosis of discogenic pain (a.k.a. internal disc disruption and or IDD) must be ruled out by a technique called provocative discography.
In a nutshell, this procedure (which is really an art) calls for the examiner to place a needle into the center of the suspects disc and pressurize it by injecting a contrast dye (which will show up bright white on fluoroscopy/CT). If, upon injection, that disc re-creates the patient's exact pain (concordant pain), then it is more likely than not that the disc is the cause of the patient's pain. More specifically, the annular tear that allows the contrast to reach the nerve-rich outer fibers of the annulus is the cause of the pain. However, we are not quite finished with the procedure: the examiner will then repeat the procedure on the disc above, which in this hypothetical case looks perfectly normal on MRI – not even any degenerative change. It is hoped that this disc will not create any pain at all. If that is the case, then provocative discography has successfully confirmed the patient has discogenic pain coming from the target disc. In an ideal world, the patient now undergoes a CAT scan in order to visualize the size and location of the annular tear.
Provocative discography is an art! Only the most skilled physicians can correctly perform this procedure. For example, all discs will become painful upon injection if they are pressurized over a certain amount. Another tricky situation arises with the patient who suffers a grade 5 (see below) annular tear which cannot hold pressure. In this case, the patient may not experience any pain, even though the contrast dye flows right out of the disc upon injection.
Is It Safe? one of my concerns about any needlestick injury to the disc (discography certainly included), was that such an injury would result in a train of degenerative events--like is does with sheep and rat discs [5, 27, 28, 29, 30]--that would ultimately lead to the development of a symptomatic annular tear and/or disc herniation, which in turn could lead to discogenic back pain and/or leg pain.
HOLD THE PRESS! in 2009, Carragee reversed his opinion on the long-term effects of needlestick injury in an incredible investigation (it won the prestigious ISSLS Prize that year). More specifically, this all Stanford team of researchers reported the results at the 10 year time point of a prospective study in which 75 subjects without serious low back pain initially underwent MRI and discography in 1997. As a control group, 75 subjects--none of whom had any pain--were matched to the experimental group with regard to gender, job and body morphology; they all underwent MRI scans but did not undergo discography. At the 10 year time point, another MRI was performed on all participants. The results were surprising (not to me): unlike the four-year Carragee study (which showed no ill effects from discography stick), this time there were big, statistically-confirmed differences between the two groups. More specifically, the discs that had been exposed to puncture and injection had a greater progression of degenerative findings compared to the control (non-injected) discs. With regard to new disc herniation, there were 55 new herniations in the discography group compared to only 22 in the control group (p = 0.003), and these herniations "were disproportionately found on the side of the annular puncture (p = 0.0006). Furthermore, disc height loss as well as a loss of disc signal also was greater in the discography group. Carragee concluded, "Modern discography techniques using small gauge needle and limited pressurization resulted in accelerated disc degeneration, disc herniation, loss of disc height and signal and the development of reactive endplate changes compared to match-controls. Careful consideration of risk and benefit should be used in recommending procedures involving disc injection." I told you so!
When it comes to diagnosing discogenic pain, provocative discography with CT assistance is the proverbial gold standard. The Dallas Discogram Classification System was originally described in the late 1980s (126,118), but has since been modified twice.
Here's a summary of the 'Original Dallas Discogram Classification System':
Grade 0: Normal non-leaking nucleus - all the contrast material stays within the nucleus after injection.
Grade 1: Annular tearing confined to the inner region of the annulus fibrosis - Fig. #1 demonstrates what this might look like on axial CT imagery (although the needle that delivered the contract material into the center of the disc would be long-gone by this time). Note the needle has injected a radio-opaque dye (pink) into the center of the disc (nucleus) which is used as a 'marker'. At about 5 O' Clock (black arrow) a 'tear' or 'fissure' has become visible from the leakage of some contrast material. It extends from the nucleus radially into the inner 1/3 of the annulus fibrosus. This fissure would probably not be painful since there are usually no pain fibers in this region. This could be described as a 'Grade 1 Radial Annular Tear', or Grade 1 Internal Disc Disruption (IDD).
Grade 2: Annular tearing has completely disrupted the disc but has NOT affected the outer contour of the annulus, i.e., no leakage, no bulging, or no herniation - Figure #2 demonstrates that there has been a progression or worsening of the annular tear/fissure. Now the entire annulus has been disrupted (torn through), except for the very outer fibers and the PLL (blue) as denoted by the pink contrast material that has now moved from the nucleus through the annulus. Note that there is no leakage of dye from the disc, nor is there any bulging or protrusion of the disc. This would be classified as Grade 2 IDD or a Grade 2 radial annular tear. Despite no compressive effect on the right nerve root (yellow) (which later converges into the sciatic nerve), many of these patients (suffering Grade 2 IDD) suffered lower back pain which traveled into the lower limb and even past knee into the lower leg and foot.
The 'Modified Dallas Discogram Description' was finalized in the 1990's and is the 'Gold Standard' for the CT classification of annular tears. It was initially developed by a group of researchers from Texas (as described above in detail) (126), 'modified' by Bogduk et al. (7) in 1992, and then finally modified by Schellhas et al. in 1996(15). Below is a brief look at what that system looks like: (Sorry for getting off topic here!)
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