Thanks to the
The Back Letter July, 2000 for premission to reproduce this article!
Award-Winning Study Finds That Current Diagnostic Techniques Cannot Identify Pain of Discogenic Origin
This year's Volvo Award for clinical research honors a study that raises new doubts about the ability of current diagnostic techniques to identify painful annular tears and discogenic pain.
The study found that high-intensity zones (HIZs) on MRI scans--even when accompanied by a positive discogram--are not reliable indicators that pain stems from the disc. "For better or for worse, the identification of an annular tear has been one of the main tools used to diagnose the cause of low back pain, and now it looks like it's a false start in many patients," said Eugene Carragee, MD, lead author of the new study.
"After 100 years of searching, the diagnostic, pathoanatomic marker for chronic low back pain illness remains undiscovered," said Carragee. "The spines of patients with chronic low back pain and asymptomatic individuals are not so different." (See Carragee et al., 2000.)
Carragee says that he personally believes that annular fissures may be the cause of some forms of low back pain. However, he suggests that what distinguishes self-limiting back pain from severe, disabling low back pain illness may not be physical pathology. "I think that those with annular fissures and low back pain of no consequence may not have different spinal pathology than people with severe low back pain illness," Carragee suggests. "However, their coping mechanisms, emotional responses, and social circumstances may be very different."
The problem with current diagnostic tests such as discography and magnetic resonance imaging, says Carragee, is that they cannot reliably indicate where the pain is coming from. And they cannot identify the nonphysical factors that may be contributing to the patient's illness behavior.
Carragee presented the new study at the annual meeting of the International Society for the Study of the Lumbar Spine in Adelaide, Australia. Although the study called into question the diagnostic techniques of many clinicians in attendance, reaction was largely positive. "It is a wonderful study" said Gunnar B. J. Andersson, MD, of Rush-Presbyterian-St. Luke's Medical Center in Chicago.
For those new to this area, annular fissures in the disc often appear as "high-intensity zones" on MRI scans. Clinicians who believe these fissures may be a source of discogenic pain often attempt to confirm this suspicion by performing provocative discography. Unfortunately, it would appear that neither of these diagnostic techniques--singly or in combination--can accurately show that the target disc is the source of the patient's low back pain.
Carragee et al. studied 42 patients with low back pain and 54 asymptomatic individuals. All of the symptomatic subjects were patients with "chronic back pain illness" undergoing assessment to see if they were candidates for fusion surgery. The asymptomatic subjects included individuals with and without disc degeneration, with and without other forms of chronic pain, and with and without an abnormal psychological profile.
The asymptomatic subjects included 20 individuals who were free of back pain after lumbar discectomy, 10 patients who had chronic neck and arm pain following cervical discectomy, 10 persons who were pain-free following cervical discectomy, eight iliac bone crest donors (with iliac crest donor site pain, but no back pain), and six patients with a psychiatric diagnosis (somatization disorder).
All subjects underwent physical examination, psychometric testing, plain x-rays and MRI, and provocative discography. Discography was performed and graded by blinded observers, according to the protocol of Walsh et al., previously described in the BackLetter and elsewhere. (See Walsh et al., 1990.) The identification of HIZs was performed according to a standardized protocol, with the HIZs identified by experienced, blinded readers. (This study will be published in the journal Spine later this year; see study for details.)
A total of 109 discs were evaluated in the symptomatic group and 143 in the asymptomatic group. The results raise questions about both diagnostic tests.
"There were a lot of high-intensity zones in the symptomatic group" said Carragee. Fifty-nine percent of the symptomatic group had a high-intensity zone on MRI. "But almost a quarter (24%) of asymptomatic patients had an HIZ," he added.
Seventy percent of the HIZs in both groups tested positive on discography according to the Walsh criteria. Pain intensity on discographic evaluation of the HIZs was similar in the symptomatic and asymptomatic groups.
One of the cardinal tests applied in clinical practice to confirm discographic findings is the confirmation of concordancy. Clinicians will ask patients if provocative discography reproduced their usual pain. A positive answer is often interpreted as confirmation that the injected disc is indeed the source of a patient's symptoms.
This study suggests that concordancy cannot reliably discriminate between symptomatic and asymptomatic individuals. "Upon discography, 100% of the subjects with an HIZ in the iliac bone crest group [who had iliac bone crest donor site pain, but no back pain] reported their pain to be concordant with their usual pain" said Carragee.
Overall, the study suggested that an HIZ is not a reliable indicator of discogenic pain. "The hypothesis we were testing was whether a standardized HIZ disc confirmed the diagnosis of symptomatic intervertebral disc disruption. The data did not support that hypothesis," said Carragee. "The prevalence of HIZs in asymptomatic individuals is too high for this to be a useful clinical test."
Discography did not prove capable of discriminating between symptomatic and asymptomatic HIZs. High-intensity zones were painful upon injection in both groups. "Although an HIZ is associated with a painful disc injection, it appears to be independent of chronic low back pain illness," said Carragee.
The best predictor of a painful HIZ in this study was an abnormal result on psychometric testing (tests for the presence of psychological distress). "What we showed is that the amount of discomfort that many patients have with discographic injection is most closely related to psychological and social issues" said Carragee. This suggests, according to Carragee, that low back pain may have physical, psychological, and emotional dimensions. He noted the importance of treating the whole person with hack pain, not just the anatomic abnormalities.
Several questioners brought up important points during discussion of this study. "It seems that you have found that there are symptomatic and asymptomatic annular cracks, and that some of them are associated with high-intensity zones," Andersson observed. He noted that this is not all that different than the situation with disc protrusions, where both symptomatic individuals and asymptomatic individuals have radiographic evidence of a disc lesion.
Andersson noted that clinicians discriminate among symptomatic and asymptomatic disc herniations through patterns of pain and other clinical symptoms. "We use this as our guide as to whether something should be done about these disc protrusions. Is there anything in your population that would allow us to do the same in individuals with annular crocks?"
Carragee said that he was not aware of any strategies that would allow this type of differentiation. "I think the problem is that there is no real definition of what discogenic pain is." In other words, the symptoms of symptomatic disc herniations often fall into a distinctive and recognizable pattern. This does not seem to be the case regarding fissures in the disc.
Edward Hanley, MD, of Carolinas Medical Center asked whether Carragee has any advice on the appropriate role of discography, given recent findings questioning its value. "If you believe your results, how has it changed your clinical practice, and how should it influence me?" Hanley asked. "And what should we do with all these left-over fusion cages?" he added, to peals of laughter (implying that it would be difficult to select candidates for fusion surgery employing cages if it is not possible to identify symptomatic discs).
Carragee responded that he no longer considers discography to be a useful test among patients with abnormal psychological findings or marked illness behavior. He noted elsewhere in his presentation that up to half of individuals who undergo discography probably have psychological profiles that would fall into this category.
He did say that he still finds discography to be a useful test in some patients with a normal psychological profile. "For instance, it might be useful in a patient with spondylolisthesis and a grade I slip, and a black disc above it. It might be helpful to tell you if that disc contributes to the patient's pain problem" said Carragee.
However, Carragee indicated that clinicians probably should not look for discography to provide definitive black-and-white findings in most situations. "I think there is a lot more gray than there was before."
Carragee E et al.,
Lumbar high intensity zones and discography in subjects without low back complaints,
Spine, 2000; in press.
Walsh TR et al.,
Lumbar discography in normal subjects: A controlled prospective study,
Journal of Bone and Joint Surgery [Am], 1990; 72:1081-8.
COPYRIGHT 2000 Lippincott/Williams & Wilkins