Provocative Discography: Section 1

A variety of pathologic processes affect the intervertebral disc, potentially causing noxious stimulation of nerve endings. A precision injection of contrast dye into the disc nucleus also stimulates nerve endings. The stimulus applied with discography has two components- a chemical stimulus resulting from contact between contrast dye and sensitized tissues, and a mechanical stimulus resulting from a fluid-distending stress.

The underlying premise of discography is that this applied stimulus replicates the clinical noxious stimulus responsible for the patient’s symptoms, and that reproduction of the patients clinical symptoms during the injection confirms the disc as the source of pain.

As with any diagnostic test, it is important to know the false positive and false negative rates associated with provocative discography, which are used to calculate sensitivity and specificity. Defining the false positive and false negative rates requires comparing the test results against a gold standard (1,2,3). A gold standard is a method for definitively establishing a diagnosis, and is typically obtained from biopsy, surgery, or long term follow-up (1). Unfortunately, in contrast to radicular pain, there is no absolute method to determine the tissue origin of lumbar axial pain, and therefore no way to determine the determine the sensitivity and specificity of discography.

(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.

There are a variety of factors that can lead to both false positive and false negative results from provocative discography.

One possible source of both false positive and false negative injections is that the stimulus applied with the injection may not be selective for the nerve endings in the disc being studied. The nerve endings in the lumbar disc are in the endplates and middle and outer annulus. Although pathologic processes involving the endplate can occur (1,2), the innervated portion of the disc most usually affected by pathologic processes is the annulus.

(1) Malmivaara, et al. Plain Radiographic, Discographic, and Direct Observations of Schmorls nodes in the Thoracolumbar Junctional Region of the Cadaveric Spine. Spine 1987 12:5;453-7.

(2) Hsu, et al. Painful Lumbar Endplate Disruptions: A Significant Discographic Finding. Spine 1988 13:1;76-79.

For the provocative discography construct to be valid, the injection must selectively affect the nerve endings in the annulus of the disc being studied, which is the presumed site of the clinical noxious stimulus. A number of authors have suggested alternate sources for the pain of discography, other than stimulation of annular nerve endings. Postulated pain mechanisms include increased pressure at the endplates or within the vertebral body, increased Substance P and VIP in the dorsal root ganglion, or transmission of mechanical stimulation to the facet joints.

Heggeness, et al. Discography Causes End Plate Deflection. Spine 1993 18:8;1050-3.

Guyer, et al. Contemporary Concepts in Spine Care- Lumbar Discography. Spine 1995 20:18; 2048-59.

Weinstein, et al. The Pain of Discography. Spine 1988 13:12;1344-8.

Despite these hypotheses, there is good evidence that the provocative response resulting from discography is related to stimulation of nerve endings in the outer annulus, rather than other factors (1,2,3). Although relatively unusual, painful endplate disruptions can also occur (4).

(1) Vanharanta, et al. The Relationship of Pain Provocation to Lumbar Disc Deterioration as seen by CT/Discography. Spine 1987 12:3;295-98.

(2) Moneta, et al. Reported Pain during Lumbar Discography as a Function of Annular ruptures and Disc Degeneration. Spine 1994 19:17;1968-74.

(3) Derby, R. The ability of pressure controlled discography to predict surgical and non-surgical outcome. Spine, in press.

(4) Hsu, et al. Painful Lumbar Endplate Disruptions: A Significant Discographic Finding. Spine 1988 13:1;76-79.

The complex nature of anatomic structures can also lead to inaccurate results from discography. Anatomic structures are typically composed of several different types of tissues. A pathologic process can potentially affect just one component of a structure, which may not be the same component targeted by a precision injection. For example, discogenic pain is commonly felt to be a result of annular fissures originating in the nucleus and extending to the outer annulus, which is where the majority of the discs nerve endings reside. During discography, contrast is injected into the nucleus. If there are no fissures, the contrast will be confined to the nucleus. However, histologic studies have demonstrated that there can be middle or outer annular abnormalities that are not contiguous with the nucleus (1). In such cases, an injection into the nucleus could lead to a false negative result, while an annular injection could be diagnostic.

(1) Gunzberg, et al. A Cadaveric Study Comparing Discography, Magnetic Resonance Imaging, Histology, and Mechanical Behavior of the Human Lumbar Disc. Spine 1992 17:4;417-423.

Another potential source of inaccurate results from discography is the change in CNS nociceptive processing that occurs with chronic pain.

The neuroanatomic pathways mediating acute pain behave as a hard wired system, with a pure stimulus-response relationship (1). However, these neuroanatomic pathways are plastic, as they change with the development of chronic pain. With chronic pain central sensitization occurs, and dorsal horn cell activity no longer depends on peripheral tissue injury (1,2). A pure stimulus-response relationship no longer exists. Both previously innocuous stimuli to the dorsal horn and stimuli from outside the original receptive field cause pain. As a result, the interpretation of diagnostic injections based on an acute pain paradigm may be inaccurate (2). In the presence of chronic pain, it is possible that an anesthetic injection of an injured nerve or structure may not produce complete pain relief, anesthetizing an adjacent normal nerve or structure may relieve pain, and provoking a normal structure or nerve may reproduce a patient’s clinical pain.

(1) Siddle, P and Cousins, M. Spinal Pain Mechanisms. Spine 1997;22:98-104.

(2) North, R, et al. Specificity of diagnostic nerve blocks: a prospective, randomized study of sciatica due to lumbosacral spine disease. Pain 1996;65:77-85.