The
Role of Provocative Discography In Endoscopic Disc Surgery
Anthony T. Yeung, M.D.
Introduction
Lindblom first described discography as a useful
tool to identify intervertebral disc ruptures in 1948.(1) Hirsch then
correlated the disc injection with pain reproduction.(2) Since then, with
improved understanding of the pathophysiology of
discogenic back pain, its usefulness in selecting patients for surgical
treatment has been validated and widely accepted by physicians who use it for
the clinical management of chronic low back pain.
For ten years discography was set back due to a poorly done study by Holt, who
found a 37% false positive rate using highly irritative
Hypaque transthecally in a
prison population, prompting him to conclude that discography has no value as a
diagnostic test.(3) Holt's study was repudiated 20 years later by Simmons,(4)
then Walsh,who found discography to be 100% specific,
although its sensitivity could not be determined.(5) Walsh concluded that
discography was a valid method to determine that the disc was a pain generator.
Colhoun correlated a positive discogram
with good surgical outcome (89%) in patients treated by anterior/posterior
fusion(6). Moneta found strong correlation of outer
annular tear disruption with pain provocation during discography.(7)
With the advent of minimally invasive techniques, both Saal(8)
and Yeung(9) began to use electro-thermal and radio-frequency techniques to
treat the painful annular tears. Saal utilizes a
thermal resistive catheter threaded adjacent to the inner annulus while Yeung
prefers a visualized technique that incorporates removing the degenerative interpositional disc tissue from the annular fibers.
In spite of numerous studies validating discography as a useful patient
selection tool for various treatment protocols, controversy continues,
primarily from physicians who do not perform their own discograms but rely on
others to help with patient selection, and attention given to articles that
point out the variability in defining discogenic pain and the ability to
determine concordancy in pain reproduction.
The Role of Discography in Selective Endoscopic Discectomy
Since 1991, the author has performed his own discograms and has utilized
provocative discography to help identify the pathologic lesion in thousands of
lumbar discs. The endoscopic technique is used for a broad spectrum of disc
herniations as well as discogenic back pain from internal disc disruption. The discogram was not only used for pain provocation in patient
selection, but also to stain the degenerated disc material, annulus and
epidural tissue that would come in contact with the non-ionic water soluble discographic material (isovue M
200). A vital dye, (indigocarmine) was added to the
radiographic agent (1-2cc mixed with 9cc isovue). The
indigocarmine would selectively stain the acidic
degenerative disc tissue and would outline the annular tears in the disc and
annulus. An endoscope with distal irrigation was then utilized to visualize the
disc tissue and annular tissue surrounding the annular tear.
It was soon recognized that discographic findings
were more sensitive than MRI in identifying the presence of a painful abnormal
disc, and degenerative disc tissue could be selectively removed, preserving
normal disc tissue, which had a different endoscopic look and consistency. The discogram was able to identify the type, location, and
extent of the radial and circumferential tear as well as help in identifying
the type of disc tissue involved in the herniation. A large collagenized
fragment or an endplate fragment would be seen as a void in the discogram, whereas a soft disc herniation would be stained
through out. Lateral tears connecting with the exiting nerve root could be
visualized with discography, but invariably missed by the MRI
Pain Provocation
With the surgical technique relying on a discogram
to label the targeted disc material in every endoscopic discectomy, the author
had the opportunity to compare a patient's reaction to the discogram
provocation with his response with and without sedation. Pre-operative
discography performed for the purpose of identifying the painful disc amenable
to techniques of selective endoscopic discectomy and thermal annuloplasty
required two concomitant findings. The discogram
pattern had to be abnormal in identifying the disc structure causing the pain,
and pain provocation must be severe. enough to warrant the risks of endoscopic
disc surgery. For the purposes of pain reproduction, the patient was asked to
describe the pain using analog scale of 1-10
separately for back and for leg pain. Only pain scale numbers 5 or more were
considered clinically sufficient for surgical intervention. The patient was
also asked to describe his pain as concordant , similar, or discordant. The
procedure was always done without sedation and with only the skin anesthetized.
If the patient had pain reproduction, but the disc morphology was considered
normal, this was insufficient to be considered a positive discogram
for surgical purposes. If a patient had an abnormal discogram
pattern, but did not have pain reproduction level 5 or higher, this was
considered insufficient for surgical intervention. The discogram
pattern was described in accordance to the degenerative stages as calssified by Adams(10) and the extent of the radial tear
by the Dallas Discogram Description(11). The
circumferential component was divided into quadrants of involvement in the
absence of a post discogram CT scan. This method of discogram classification was utilized as an integral part
of the YESS technique for selective endoscopic discectomy.(12). Other unusual
patterns were described separately as endplate separation, intranuclear
herniation into the end plate, radial tear communicating with the thecal sac, or simply unclassificable
due to complete uptake of the dye through venous channels.
Concordancy Versus Non-Concordancy
It was soon recognized that the requirement of concordancy
versus non concordancy was an exercise in futility,
as the unanesthetized patient was usually too
traumatized by the severity of pain reproduction that he could not tell
immediately whether the pain was concordant or not. The usual response was the
reproduced pain was much worse than his usual pain, yet the results of surgery
eliminated his usual pain post operatively. Therefore, much of the controversy centers on defining what is discogenic pain and the
requirement of concordancy to validate the test.
Patients with a low pain threshold ,with drug dependency, or suspected psychologic factors requiring complementary treatment or
who would be poor candidates for any surgical treatment could be easily
identified by the way they responded to the discogram
process itself. Patients who could not tolerate the needle puncture into the
skin or could not tolerate the pain of needle insertion into the annulus would
be considered poor candidates for any surgical intervention. These patients
would also be unable to relay information about pain concordancy.
If a patient was sedated for surgery, He would usually report less pain on the analog scale while sedated than when he underwent his
provocative discogram pro-operatively. The pain
reproduction would usually be cut in half while sedated.
Clinical Use of Provocative Discography
The author has treated over 1700 discs in over 1000 patients using
discography as an integral part of the endoscopic procedure. Discography has
helped with patient selection, and as a guide to intradiscal pathology.
Visualized pathology could be probed and studied in a conscious patient, and
herniations could be targeted by following the stain.
The role of provocative discography extends beyond patient for fusion. With
emerging new minimally invasive techniques for treating discogenic pain, the
ability to identify the pain generators in the lumbar disc will enhance
development of techniques for annular healing and augmentation, nucleus
replacement, and endoscopic stabilization of the disc.
To do so, discography will become an integral part of the process, and it is
imperative the the literature of the future be by
surgeons who are capable and interested in performing their own discography in
order to avoid the inter-observer variability that confuses the reader of
scientific articles that raises doubts about the role of discography simply
because there is no real definition of discogenic pain.(13) For the time being,
until we can standardize the definition and perform discography in a
standardized manner, the best option to improve patient selection is to
encourage rather than discourage physicians who use discography for patient
selection to do their own discography. That way, there can never be a false
positive discogram, only a false interpretation of a
painful discogram.
References