Discography is a diagnostic test in which radiographic contrast is injected into the nucleus pulposus of the intervertebral disc. Although originally developed for the study of disc herniation, discography is now used most commonly to identify symptomatic disc degeneration. There are two components of discography: (a) the anatomic appearance of contrast spread within the disc (using plain radiographs and/or computed tomography [CT]) and (b) the presence or absence of typical pain during contrast injection within the disc (pain provocation). The usefulness of discography remains controversial, and the last several years have seen an increase in the level of this controversy. Some clinicians continue to routinely use discography to identify symptomatic discs prior to surgical fusion, while others believe the test is of unproven benefit in identifying symptomatic discs. Discography remains the only test available that attempts to correlate pain response from the patient during provocation with abnormal discs discovered on imaging studies. Improved surgical outcomes following lumbar fusion have been reported when guided by the use of discography. However, a recent 10-year retrospective case-control study suggested that patients who underwent diagnostic discography had accelerated disc degeneration, disc herniation, loss of disc height and signal, and the development of reactive endplate changes compared to match-controls involving the control (normal) disc involved in the diagnostic discography procedure. Intradiscal electrothermal therapy (IDET) is a minimally invasive procedure that offers an alternative treatment to a subset of those patients with discogenic low back pain. Much like its use prior to fusion, discography is used to identify symptomatic intervertebral discs prior to IDET. During the past few years, close examination of the existing evidence has produced conflicting results, as the available controlled trials of IDET have produced conflicting results. The use of IDET in the treatment of symptomatic degenerative disc disease has declined dramatically in recent years. A description of IDET has been retained in this edition, as the technique remains available for clinical use. Several other intradiscal techniques have emerged, but the available evidence remains inconclusive. Among these techniques is plasma disc decompression (PDD), a technique that uses radiofrequency technology to reduce intradiscal pressure and treat patients with persistent radicular pain associated with small, contained disc herniations and disc bulges. One controlled trial is now available for this treatment technique and it is described in this chapter. Symptomatic degenerative disc disease remains common and the available treatments are unsatisfactory; undoubtedly, new intradiscal techniques will be developed in the near future.

The intervertebral discs are comprised of glucosaminoglycans with a relatively fluid inner nucleus pulposus surrounded by a stiff, lamellar outer annulus fibrosis. With aging, the hydration of the intervertebral discs declines, leading to loss of disc height and fissure formation in the annulus fibrosis. These fissures begin centrally near the border between the nucleus pulposus and the annulus fibrosis and can extend to the periphery of the disc space. This process of degradation is called internal disc disruption and is believed to be responsible for producing discogenic pain. These same radial fissures within the annulus represent paths through which nuclear material can pass and extrude as a herniation of nucleus pulposus. When this extruded material is adjacent to an exiting spinal nerve, it can lead to intense inflammation, spinal nerve compression, and radicular pain with or without radiculopathy (spinal nerve dysfunction in the form of numbness, weakness, and/or loss of deep tendon reflexes).

The lowest three lumbar intervertebral discs (L3/L4, L4/L5, and L5/S1) are most commonly associated with discogenic pain. The disc spaces at these levels can be entered safely using an oblique approach by placing a needle that passes near the junction of the transverse process and the superior articular process of the vertebra bordering the inferior aspect of the disc space to be studied. The needle then passes medially and inferior to the exiting spinal nerve to penetrate the posterolateral aspect of the annulus en route to the center of the disc space (Fig. 9-1). The L3/L4 disc space lies close to the axial plane, whereas the plane of the L4/L5 and L5/S1 discs follows the lumbar lordosis and is angled progressively in a cephalad-caudal direction. A clear grasp of the plane in which each disc is typically found and accurate alignment of the C-arm are essential to carrying out discography safely and successfully.

The patient with low back or neck pain originating from the vertebral disc often presents with deep, aching, axial midline pain. Pain can be referred to the buttocks and posterior thigh from lumber discs but does not extend to the distal extremities. Patients with discogenic pain are often young and otherwise healthy; discogenic pain is common in those with jobs that require repetitive motion of the affected spine segment (e.g., package handlers) or that expose the spine to excessive vibration (e.g., longdistance truck drivers, helicopter pilots, jackhammer operators). Onset of symptoms is usually gradual. Pain is experienced with prolonged sitting (sitting intolerance), standing, and bending forward. The referred pain usually remains in the proximal part of the extremity. Results of physical examination are nonspecific, with limited range
of motion at the affected segment or pain with movement, particularly on flexion. Magnetic resonance imaging (MRI) and CT reveal only nonspecific findings, such as loss of disc height and/or hydration; these findings are often present without pain. The presence of a highintensity zone on MRI at the posterior aspect of the disc indicates that a radial tear or fissure may be present in the annulus fibrosis, a nonspecific finding commonly found in those without back pain. Treatment for discogenic pain starts with conservative therapy, including physical therapy and oral nonsteroidal anti-inflammatory drugs (NSAIDs). In those with prolonged or disabling pain that is suspected to be of discogenic origin, provocative discography can help identify the affected level and guide targeted therapy. Patient selection for IDET and PDD is critical to assuring any benefit, as both procedures have shown modest benefits but only in highly selected patients. The selection criteria for these two intradiscal treatment techniques are discussed in the sections describing the techniques below.

The use of diagnostic discography has evolved rapidly in recent years. The addition of pressure monitoring during injection has become widespread and undergone careful scientific validation, and a number of more recent clinical trials have incorporated discography into patient selection criteria for treatment. Yet, the usefulness of this diagnostic test remains in question: advocates point to the fact that pain on provocation is highly suggestive as the disc as a source of pain and critics emphasize the subjective nature of the test and lack of a gold standard for validation. Emerging evidence from retrospective study suggests that there is accelerated disc degeneration within the disc that was previously normal (the control disc) over the decade following diagnostic discography. There are no definitive answers, but the controversy has led to a decline in the use of discography as a diagnostic test. Nonetheless, many practitioners and clinical investigators still rely on discography as the best available means to select patients with symptomatic degenerative disc disease for targeted treatment.

In no area of interventional pain is disagreement more apparent than when discussing expert recommendations regarding use of diagnostic discography. The American Pain Society (APS) Low Back Pain Guideline Panel published a report in 2009, concluding, “In patients with chronic nonradicular low back pain, provocative discography is not recommended as a procedure for diagnosing discogenic low back pain (strong recommendation, moderate-quality evidence).” Subsequently, the American Society of Anesthesiologists (ASA) Task Force on Chronic Pain Management published A 2010 Practice Guideline, offering the following recommendation: “Provocative discography may be considered for the evaluation of selected patients with suspected discogenic pain; it should not be used for routine evaluation
of a patient with chronic nonspecific back pain.” Both guideline panels considered the same body of scientific evidence. The APS group cited the lack of any available gold standard against which to validate discography and the significant complications associated with the test, while the ASA group focused on the small number of uncontrolled trials suggesting that discography allows for improved patient selection for invasive treatments, including surgical lumbar fusion.

IDET has also been the subject of much debate. Two moderate-sized RCTs appeared during this decade, one demonstrating modest long-term reduction in back pain in a subset of patients and a second showing no benefit when compared to sham treatment; both trials were limited to patients with early degenerative disc disease at a single disc who reported concordant symptoms during discography. Several observational trials do suggest modest reduction in pain after treatment with IDET. The 2009 APS Low Back Pain Guideline Panel concluded, “IDET may be considered for young active patients with early single-level degenerative disc disease with well maintained disc height.” The 2010 ASA Task Force on Chronic Pain Management made the following recommendation: “There is insufficient evidence to adequately evaluate benefits of … intradiscal electrothermal therapy (IDET) … for nonradicular low back pain.” Despite the suggestive evidence that IDET may provide some pain reduction in young, active patients with early degenerative disc disease, many third party payers in the United States have eliminated reimbursement for this treatment and there has been a sharp decline in its use.

There are a number of emerging treatments for discogenic pain including the application of thermal energy to the annulus, injection of growth factors within the nucleus pulposus, or the injection of fibrin “glue” within the central disc: All await clinical validation. While no recommendations can be made about these treatments today, it seems more likely than not that some form of therapy requiring percutaneous access to the intervertebral discs will emerge from current scientific development efforts. Thus, the skills needed to place a needle within the intervertebral disc that are described in this chapter are likely to remain a core part of the skill set of interventional pain specialists.

Among intradiscal treatments that have undergone direct clinical validation, PDD is among the few, and thus it has been included in this discussion of intradiscal treatments. A single multicenter trial comparing the efficacy of PDD with transforaminal injection of steroids was conducted in patients with small, contained disc herniations and persistent radicular pain. The trial showed sustained reductions in leg pain and improvements in physical function during the 2-year follow-up period that were superior in those treated with PDD when compared to those receiving transforaminal steroid injections. It is important to emphasize that the group treated was highly selected: patients with small (<3 mm) disc protrusions and predominance of ongoing leg pain. Most patients with such small disc herniations are asymptomatic, and this group represents just 5% to 10% of patients with radicular symptoms. It is also important to emphasize that PDD is not meant to be used for the treatment of discogenic pain.