Chapter 64 Discography Flashcards
Discography has been called
a “test in search of an indication,” and a “solution in need of a problem
Pain originating from the spine commonly manifests as
pain in the
low back and neck, and less frequently as pain
in the mid-back.
Several factors make the identification of spinal
pain generators challenging
First, back pain can originate
not only from various spinal column components, but can
also be referred from structures adjacent to the spine such as abdominal or pelvic viscera, sacroiliac joints, and so on. Second, pain can be difficult to localize due to multisegmental, predominantly autonomic spinal innervation, with resultant convergence in the spinal cord. The diagnosis of spinal pain is further complicated by the concurrent presenceand overlapping clinical features of various spinal disorders, especially degenerative conditions.
term internal disc disruption (IDD)
to describe a disc that is considered the main
source of patient’s pain but appears functionally intact on spinal imaging
Isolated degenerative
disc pathology
one or two discs show profound degeneration in the presence of other relatively normal appearing discs
discogenic pain (DP)
describes a clinical
state in which the disc is considered a main source of a
patient’s spinal pain
A normal disc
grossly compartmentalized
into nucleus pulposus (NP) and annulus fibrosus(AF). Interspersed in an abundant intercellular matrix in the two disc compartments are sparsely present cells. The cells populating the NP are chondrocyte-like, while those
comprising the AF are fibrocyte-like.3 The intercellular
matrix in the NP is a “jelly-like” substance containing high concentrations of water and proteoglycans, while the matrix in the AF consists predominantly of Type I and
II collagen fibers.
The compressive forces
applied to the disc are borne directly by the
NP, and are distributed as a tensile force to the annular collagen
The incompressibility exhibited by a normal NP is due to its
high water content, which in turn is maintained by the
hydrostatic pressure generated by proteoglycans
The normal NP proteoglycan content is a function of the
delicate balance between
anabolic and catabolic enzymatic
activities.
The vascularity of a normal intervertebral disc
limited to the outer third of the AF. In addition, the disc is separated from the vascular vertebral body by avascular cartilaginous end plates.
Consequently, the metabolic needs of the NP and inner AF are met almost entirely by
diffusion from the capillary plexuses in the adjacent vertebral bodies and outer AF. This process is facilitated by circadian changes in intradiscal pressure; lower nighttime pressure facilitates the flow of fluids into the disc, while higher daytime pressure forces the fluids out of the disc.
The end
products of the NP cellular metabolic activities are also
removed by
the diffusion. the disc lacks scavenger cells, so that degradative products tend to accumulate over time, which can interfere with normal homeostatic
functions.
The innervation of the normal disc
predominantly limited to the outer third of the AF. Disc innervation is mostly in the form of mechanoreceptors, which originate from plexuses along the anterior and posterior longitudinal ligaments. The posterior plexus receives its input from the sinuvertebral nerve and gray rami communicans, while the anterior plexus receives contributions mainly from gray rami communicans.
degenerated disc disease most likely the result of
a decline in the number and function of viable disc cells, enhanced matrix
metalloproteinase (MMP) activity, and increased activity
of discal cytokines and other proinflammatory mediators. These metabolic derangements can result in a reduction of nuclear proteoglycans and loss of discal water content.
The diminished NP hydrostatic pressure leads to
increased NP compressibility, which exposes the AF to direct compressive forces.
In addition to mechanical stress, the AF
also undergoes degenerative changes similar to the NP.
These combined insults result in
the loss of annular collagen,
mechanical failure, and the development of annular
fissures that spread outward towards the periphery.
Annular fissures
hallmark of discogenic pain. These tears are zones of highly vascularized and richly
innervated granulation tissue. The two types of nerve
fibers found in these granulation zones are vasoregulatory nerves that accompany neovascularization, and free nerve endings high in substance P concentration
“chemically sensitized.”
state has been linked to the painful response associated with minimal pressure
elevation. annular tears are abundant in mononuclear cell infiltrates, which release nerve growth factors that contribute to nerve in-growth and accelerated degeneration. Disrupted discs also contain high concentrations of pro-inflammatory mediators, which serve to sensitize nerve endings and maintain a state of hyperalgesia
In the long-term, changes in the disc morphology may
alter spinal mechanics, increase stress on adjacent spinal structures, and lead to sclerosis and auto-fusion. This
may lead to further disc and vertebral end plate degeneration, sacroiliac and facet joint pathology, and spinal
stenosis.
The rationale for discography is based on three factors
the high prevalence of spine pain, the high prevalence rate of abnormal MRI findings at asymptomatic levels, and the low success rate for surgical interventions for degenerative spondylosis.
the main criticism surrounding discography is the
high rate of false-positive (FP) results
The issue of “false-negative” discograms has received far
less attention, but can lead to
inaccurate diagnoses, unnecessary interventions, and withholding beneficial treatment(s) from otherwise good candidates.
several reasons
for this phenomenon of “false-negative”
failure to detect an inadequate
rise in intradiscal pressure because of the lack of pressure monitoring, injecting too slow, excessive sedation,
overzealous use of local anesthetic, and extensive contrast extravasation in severely degenerated discs.
