Provocative Discography: Section 3

The asymptomatic subjects studied by Walsh were all healthy volunteers, with an average age of 23. Caragee recently expanded on Walsh’s study of asymptomatic subjects, by studying a cohort of subjects who did not have low back pain, but whose clinical characteristics more closely matched those of patients with low back pain who typically present for discography.

Caragee, et al. The rates of false positive discography in select patients without low back complaints. Spine, in press.

30 subjects with no history of low back pain were recruited: 10 had previous cervical surgery with good results, 10 had the same surgery but had persistent chronic pain, 10 had primary somatization disorders. Lumbar discography was performed and interpreted according to Walsh’s protocol. Four somatization patients dropped out prior to beginning the study and two stopped the study after only one or two discs were injected, and therefore were not included in the study analysis.

Among the subjects with good results from previous cervical surgery 7/10 had at least one disc that had an outer annular rupture (10/30 discs total), while only 1/10 had a positive result. The patient with a positive test had a high Zung depression score..

Among the subjects with chronic pain 5/10 patients had at least one disc that had an outer annuluar rupture (11/32 discs total), with 4/10 having at least one positive disc. Of the 11 discs with significant structural abnormalities, 7 were positive and four were negative.

Among the subjects with somatization disorder ¾ had at least one disc that had an outer annuluar rupture (6/13 discs total), with ¾ having at least one positive disc. Of the six discs with significant structural abnormalities two were positive and four were negative

Post injection pain flare.

Based on this data Caragee concluded that in individuals with normal psychometric and without chronic pain the rate of false positives is very low if strict criteria applied, and that the false positive rate increases with increased annular disruption.

Caragee’s study is important for a number of reasons. First, it confirms Walsh’s finding that in subjects without a history of low back pain, and without psychosocial risk factors, provocation of a significant pain response with discography is unusual, with an incidence of 0% in Walsh’s study and 10% in Caragee’s study. It also confirms Walsh’s finding that although discs in this population are often structurally abnormal (combining the studies,12/20 had at least one structurally abnormal disc) they are no more likely to be positive than a structurally normal disc.

More importantly, Caragee’s study reveals that in subjects without a history of low back pain, but with a history of chronic pain or a somatization disorder, provocation of a significant pain response with discography is common, with an incidence of 40% in the chronic pain group, and 75% in the somatization disorder group. Furthermore, the more disrupted the annulus is, the greater the chance of a positive response.

Caragee’s study is a powerful reminder of the importance of psychosocial factors in modulating pain, while also demonstrating the potential of false positive responses with discography. However, in assessing the importance of this information, it is necessary to reconsider the premise of discography.

The premise of discography is that reproduction of a patients clinical symptoms during the injection identifies the disc as the source of pain. The rationale for it’s use is that the results can help discriminate among the various structures that may be responsible for axial pain. Therefore, to establish its validity, the criteria for a true positive disc must be determined in the relevant population, which is back pain sufferers. Walsh’s data on patients with chronic low back pain demonstrated that is common for patients undergoing discography to have intense pain that is very different in location and character from their clinical symptoms. In Walsh’s study the criteria for a positive test in the chronic low back pain population required that provoked pain be similar to the patient’s clinical symptoms. Unfortunately, without a gold standard for axial pain, the validity of incorporating measures of familiarity of pain into the criteria for a positive test cannot be precisely defined (1).

Caragee has clearly demonstrated the potential for false positive responses with discography. However, given the premise of discography, and the fact that patients with chronic low back pain frequently have intense but atypical pain during discography, it is difficult to know the significance of any pain response in an asymptomatic subject.

While the sensitivity and specificity of provocative discography cannot be precisely defined, it is important to remember that the ultimate criterion for a diagnostic test is whether the patient is better off as a result. If a test can predict the response to treatment, and is reliable and reproducible, then it may be clinically useful (1), even without a defined sensitivity and specificity.

(1) Sackett, et al. Clinical epidemiology. A basic science for clinical medicine. Second edition. Little Brown and Company, 1991.

(2) Jaeschke, et al. User’s Guides to the Medical Literature. III. How to Use an Article about a Diagnostic Test. A. Are the Results of the Study Valid? JAMA 1994 271: 5; 389-391.

(3) Jaeschke, et al. User’s Guides to the Medical Literature. III. How to Use an Article about a Diagnostic Test. B. What are the Results and Will They Help Me in Caring for My Patients? JAMA 1994 271:9; 703-707.