CHAPTER 16 Discography

Provocative discography is a diagnostic test sometimes used to evaluate the disc as a potential source of persistent back and neck pain syndromes. In its simplest form, provocative discography is an injection into the nucleus of an intervertebral disc, and the test result is determined by the pain response to this injection. If the injection reproduces the patient’s usual pain, some authors have proposed that the “cause” of the axial pain syndrome can be ascribed to that disc—that is, primary discogenic pain.

In 1948, Lindblom ¹ originally reported discography as a method to identify herniated discs in the lumbar spine by injecting contrast medium into the disc and following the outline of contrast medium into the spinal canal. It was noted as only a secondary consideration of the test that reproduction of the patient’s usual sciatica sometimes occurred during the disc injection. It was observed later that back pain was sometimes reproduced during the injection, as opposed to sciatica. Eventually some clinicians began using the test to evaluate discs as the source of axial pain in patients without radicular symptoms.

Since the early use of discography, it has been unclear whether reproduction of pain with injection indicated that the injected disc is the true primary source of clinical back pain, or whether the injection had simulated the usual pain in an artificial manner. Over time, attempts have been made to determine the specificity of the test and to refine the technique to reduce the risk of false-positive or false-negative results. Still this test remains highly controversial. Even the staunchest proponents of the procedure state that “discography is a test that is easily abused.”² Basic diagnostic test assessment has found fundamental problems with test reliability (i.e., does the test give the same result on repeated testing?) and validity (i.e., does the test prove what it purports to prove?). Also, it has not been shown that using the test improves the outcomes in patients receiving the test compared with patients not receiving the test. More recently, the long-term safety of disc puncture and injection has also been questioned. This chapter discusses the rationale and technique of provocative discography when used in patients with primary axial pain syndromes.

Clinical Context

Back and neck pain are very common, and in most cases determining the “cause” of a specific episode of back or neck pain is unimportant because these symptoms frequently resolve in a short time or do not seriously interfere with function.¹ Provocative discography may be described as representing a tertiary diagnostic evaluation, which should be considered only in a select group of patients.

A primary diagnostic evaluation usually involves screening for serious underlying disease (“red flags”) by history and physical examination aimed at detecting systemic disease, spinal deformity, and neurologic loss. In most patients, these examinations are negative, and nonspecific treatment alone is recommended.

In a patient who does not recover good function in 6 to 12 weeks, a secondary diagnostic survey may be indicated. This follow-up evaluation should identify serious psychosocial barriers to recovery (“yellow flags”) and definitively “rule out” serious conditions that may result in neurologic injury; structural failure; or progression of a visceral disease, systemic infection, or malignant process. Diagnostic tests for serious structural disease, including blood tests and imaging studies, have become so sensitive that these serious conditions are usually identified in the early stages.

Establishing a more specific pathoanatomic diagnosis than “nonspecific back pain syndrome” or “persistent back pain illness” becomes important only if specific therapy directed to common age-related structural changes is considered because of continued serious symptoms and functional loss. At this point, if the primary and secondary evaluations have revealed neither serious structural pathology nor significant confounding psychosocial or neurophysiologic factors, a tertiary diagnostic evaluation may be undertaken. This evaluation may occasionally uncover a clear degenerative cause of symptoms, such as unstable spondylolisthesis or progressive degenerative deformity such as an unstable degenerative scoliosis.

The most common structural degenerative changes (e.g., loss of disc height, loss of nuclear signal, minor facet arthrosis, annular fissures) may be very difficult to reconcile with the severity of apparent symptoms and pain behavior, however, because many people with minimal or no spinal symptoms have similar mild degenerative findings. The question is why do individuals with such benign findings sometimes report severe and persistent pain and impairment? The rationale of provocative discography in the tertiary evaluation is to separate anatomic spinal changes causing serious primary pain illnesses from similarly appearing common degenerative changes that do not cause serious illness. As this chapter shows, it is unclear that this goal is routinely achievable with provocative discography.

Discography Technique

Discography is performed using local anesthetic and mild sedation. The objective is percutaneous injection of a nonirritating radiopaque dye, under fluoroscopic guidance, into one or more intervertebral discs. Ideally, the central portion of the disc, the nucleus, is penetrated by a long fine-gauge needle; this is usually done from a posterolateral approach in the thoracolumbar spine and anterolaterally in the cervical spine. In the lumbar spine, the needle passes posterior to the exiting nerve root and anterolateral to the traversing root. Sometimes a bend of the needle or introducer is required to place the needle accurately, especially at L5-S1.

The passage of the needle in skilled hands should be quick and atraumatic. When the position is verified in two planes using fluoroscopy, the dye is slowly injected into the nucleus of several lumbar discs with the patient blinded to the timing and site of injection. The spread of the dye in the disc is noted on the images, and the patient’s response to injection is documented. The patient is queried at each injection, or at random intervals, whether or not the procedure is painful and is asked to rate the pain against some standardized scale (e.g., 0-5, 0-10, none-to-unbearable). If the injection is painful, the patient is asked to describe the discomfort provoked qualitatively: The injection is usually rated as exactly the same as, or similar to (concordant), or dissimilar to the patient’s usual back or neck pain.

Criteria for Positive Test

In an effort to improve the specificity of discography in diagnosing so-called discogenic pain, some investigators have used additional criteria beyond pain reproduction on injection. The criteria for establishing a positive discogram are controversial. The primary criteria for a “positive” disc injection are pain of “significant” intensity on disc injections (usually defined as ≥6 out of 10 pain scale) and a reported similarity of that pain to the patient’s usual, clinical discomfort (concordant pain). These basic criteria were proposed in the experimental work by Walsh and colleagues in 1990,²⁹ which proposed “significant pain” be defined as 3 out of 5 (or 6 out of 10) on an arbitrary pain thermometer. “Bad pain” was defined as 3 out of 5 pain, and “moderate pain” was described as 2 out of 5 pain. The authors did not stringently define concordance of pain reproduction. Some investigators have proposed additional and sometimes idiosyncratic criteria for positive injections (Table 16–1).

Test Criteria for Positive Result	Positive Test Threshold	Comments
Pain response (intensity)	≥6/10 or 3/5	Subjective and arbitrary scale. No data on reliability. Data on validity in small groups of asymptomatic subjects without psychosocial comorbidity are good (specificity >90%). Data in several studies of subjects with increased psychosocial or chronic pain comorbidity indicate validity in these subgroups is poor (specificity 20%-60%)
	“Bad” pain or worse on pain thermometer
	≥7/10
Qualitative pain assessment (concordant pain)	“Concordant pain” usually including “similar” but not exact pain	Subjective response. Data on reliability are unknown. Data on validity in small study of experimental nondiscogenic low back pain indicate validity is questionable
	“Exact” pain only
Annular disruption	Dye must show fissure to or through outer anulus	Tested only in clinical studies without follow-up to confirm outcome or other “gold standard.” Radiologic reliability best with computed tomography scan after disc injection compared with x-ray alone. Validity of additional criteria as confirming true-positive test unknown; positive injection in discs without annular disruption more common in psychologically disturbed subjects
Control disc injections	“Negative” injection (minimal or discordant pain) required adjacent to proposed “positive” disc	Injections in morphologically normal discs seem to be reliably negative even in subjects with serious psychological distress and no back pain. Reliability in other disc morphology unknown. Validity of this additional criterion as confirming true-positive test unknown
	“Normal” injection (i.e., no pain)
	Some authors insist that adjacent “control disc” must also have grade 3 annular fissure, which is “relatively painless” at equal or higher pressures than “positive disc”
Demonstration of pain behavior	Facial expressions of pain must be observed to confirm verbal pain report	Reliability and validity of this criterion as confirming true-positive test unknown
Pressure-controlled injection	Disc injections should be classified into low (<15 psi or <20 psi) or high (>50 psi) pressures at time of significant pain response; responses at pressures in between are indeterminate	Small outcomes series suggest low pressure sensitive discs are better treated with interbody fusion techniques. Reliability and validity unknown
Volume-controlled injections	“Excessive volume” or speed to injection invalidated injection	Unvalidated concept based on anecdotal evidence. Primary data unavailable to analyze
Maximum one or two positive disc injections	More than one or two positive disc injections invalidates study (all are indeterminate)	Assumption is made that generalized hyperalgesic effect may lead to multiple positive discs around single pain generator
Quantify pain tolerance by response to buffered anesthetic injection	Subjects with poor pain tolerance may not be “ideal” candidates for discography; this feature needs to be detected	It is unclear that pain tolerance to intradermal anesthetic injection is valid test to determine “pain tolerance” in patients with long-standing axial pain
Needles should be inserted from asymptomatic or least symptomatic side	Theoretically this may decrease confusion between injection and insertion pain	Some data suggest this is not an important technique. No “gold standard” confirmation was applied
Any positive disc injection must be repeated with similar outcomes before accepting result as “positive”	Intraprocedure reliability test	No data available on whether this improved or decreased test accuracy

Pain Generator Concept and Provocative Discography

The diagnosis made by a “positive provocative discogram” should indicate that the disc identified is the primary or only cause of the patient’s back pain illness, or the pain generator. This term has proven problematic, however. In a patient with persistent symptoms and a secondary workup with only degenerative findings, the task of identifying a specific isolated pain generator may be formidable. Most patients have multiple findings of disc changes and facet arthrosis, often at different levels. To distinguish which, if any, “degenerative” findings may be definitively established as causing severe back pain illness is a complex problem. Many people have occasional back or neck ache with common activities or episodic axial pain without impairment. The question is not whether any previous or possible future back or neck pain may be coming from a certain spinal structure. Rather, it may be assumed that most people with degenerative change of the axial skeleton may have occasional discomfort from several sites alone or at the same time.

The pertinent question is whether or not a suspected local anatomic structure (e.g., disc, facet, sacroiliac joint) is causing serious, disabling axial pain illness or is only a minor contributor to a generalized pain-sensitivity syndrome (e.g., fibromyalgia), a central pain-processing syndrome, an overuse syndrome related to posture or activity, or other conditions. It is hoped that some diagnostic test can identify whether or not a specific local spinal pathoanatomic structure adequately explains the severity of clinical symptoms. As a matter of practical definition, for a pathoanatomic diagnosis to be clinically relevant requires that the identified pain generator not only be capable of causing some discomfort under any circumstances (e.g., puncture and injection of a disc), but also that this structure is a primary independent cause of the patient’s apparent severe illness.

When only degenerative changes are found, it is controversial whether or not a discrete local pain generator as the cause of serious back pain illness can be commonly identified. Some clinicians believe that serious axial pain and disability can be so multifactorial (mechanical, psychological, social, and neurophysiologic contributors) that it is unreasonable to expect specific diagnostic studies to confirm an anatomic “diagnosis” for axial pain illness in every patient.³^–⁵ Even if a pain generator is suspected, it is unclear how this can be reliably confirmed to be the cause of the patient’s perceived pain, impairment, and disability in the face of complex social, emotional, and neurophysiologic confounders.

Other clinicians believe that identifying a pain generator is central to spine evaluations, is an expectation of patients, and determines the choice of treatments by focusing on the anatomic structure deemed responsible for the pain. In this model, social issues such as disability, litigation, psychological distress, and pain intolerance are believed to be secondary issues to the structural pathology.^1,⁶^–¹² These clinicians generally believe that although the history and physical examination may be helpful in suggesting serious underlying pathology such as infection and tumor, these methods are not helpful in determining the true pain generator among many degenerative structures.

Diagnostic Injections and Modulation of Pain Perception in Axial Pain Syndromes

Provocative discography relies on a patient’s subjective perception and report of pain after a progressive pressurization injection of a disc. Alternatively, a disc may be injected with an anesthetic agent with subsequent documentation of the patient’s subjective pain relief after activities that usually provoke pain. These diagnostic injections seek to identify a primary pain generator by provocative testing (stimulating a potential site of pain as in discography) or by temporary local anesthetic relief. These are subjective tests of pain perception and are subject to the effects of volitional and neurophysiologic modulation at multiple points along the neuraxis.

Many common factors are known to have potential dampening or amplifying effects on the perception of back and neck pain. These factors must be considered when evaluating the validity of diagnoses determined by diagnostic injections.¹³^–¹⁸

Adjacent Tissue Injury

Injury to adjacent tissues may increase the perception of pain in surrounding structures by a local hyperalgesic effect. This is a well-known phenomenon that occurs with any tissue damage; it may amplify pain perception by increasing local inflammatory processes with secondary neurologic sensitization in areas not directly injured, such as the area surrounding a burn or a fracture that is sensitive but without any thermal or mechanical injury. This is an important phenomenon in patients with low back pain with serious disease at one or more levels, which may sensitize the adjacent segments to provocative testing (e.g., a spine that has undergone multiple operations).^13,¹⁹

Local Anesthetic

Local anesthetic injections may decrease the perception of pain at a local site. This is the specific, active effect used in diagnostic blocks. This decrease in pain perception can also be a source of confounding effects if the exact placement of the agent is not well controlled. In addition to this direct local effect, a nonspecific placebo effect and a neurophysiologic modulation effect may occur. A relevant example is the effect of local anesthetic blockade on the perception of painful stimulus along the neuraxis proximal to the injection. A local anesthetic injection in the lower extremity may be perceived as relieving sciatica owing to disc herniation.²⁰ This is not a placebo effect (i.e., the phenomenon is seen only with an active anesthetic agent) but rather an effect on neuromodulation. This effect is important in diagnostic anesthetic blockade as a source of false-positive and false-negative findings.²¹

Tissue Injury and Nociception in Adjacent or Same Sclerotome

Tissue injury having the same or adjacent sclerotomal afferents as lower spinal elements may increase pain sensitivity at any given site. This effect is thought to be due to physiologic and anatomic changes at the level of the dorsal root ganglion or spinal cord ascending tracts. In animal models, single afferent neurons from a dorsal root ganglion may innervate three adjacent discs and a wide range of adjacent structures. This effect is important in considering the specificity of discography at sites of similar embryonic derivation to a known pathologic structure (e.g., nonunion, spondylolisthesis, painful iliac crest bone graft site). The confounding effect of this phenomenon in discography has been experimentally and empirically shown (see later).^13,²²

Chronic Pain Syndromes

Chronic pain syndromes may complicate the evaluation of low back pain syndromes. Chronic pain from regional sites near the lumbar spine (chronic pelvic pain, irritable bowel syndrome, failed hip arthroplasty) or distant to the lumbar spine (chronic neck pain, chronic headache, temporomandibular joint syndrome) may increase pain sensitivity at lower spinal elements. This effect may be regional or global and may be related to neurophysiologic changes at multiple levels along the neuraxis. Preexisting chronic pain syndromes are also associated with depression, narcotic use, and habituation, which have independent pain perception effects. This effect has been shown to have an impact on the intensity of pain intensity from discography in experimental subjects.^13,²²

Narcotic Analgesia

Narcotic medications act at multiple levels to decrease pain sensitivity thresholds, intensity, and affective response. Administration of a narcotic medication may act as a common confounder of diagnostic techniques of any type requiring accurate feedback of pain perception from a patient.^13,^23,²⁴

Narcotic Habituation

Chronic narcotic habituation may act to decrease pain tolerance in the absence of increased narcotic intake. Narcotic habituation decreases endogenous abilities to modulate peripheral nociceptive input. This effect is multifactorial. Chronic narcotic habituation is also associated with depression and sleep disturbances.

Depression, Anxiety, and Somatic Distress

Clinical depression, anxiety disorders, and increased somatic awareness may be seen as predisposing factors to chronic low back pain syndromes or reactions to the pain and disability of chronic low back pain illness or both. In either event, psychological distress usually decreases the pain threshold perception and increases perceived pain intensity and affective response.^5,^23,²⁵ These effects are likely due to central neurochemical changes and systemic effects and have been shown to affect pain responses in discographic evaluation.

Social Imperatives

Overriding social imperatives may result in a decreased pain perception or a dissociation of pain perception and functional loss. A decreased pain perception or even an absence of pain perception despite injury can be seen during some short-term stressful events, such as in accident victims, soldiers in combat, or individuals in certain training environments. Even over long periods, social and cultural factors reinforce low pain reporting and muted or absent pain behaviors.

Social Disincentive

Secondary gain issues may exaggerate pain responses of all types. When the intensity of pain behavior and report is correlated with a real or perceived social benefit or monetary compensation, the reported pain perception and pain behavior may be increased. This situation can have direct effects on provocative testing (e.g., discography) and the need for a specific anatomic diagnosis to establish social validity of an ongoing “sick role.”

Summary

When considering the diagnostic certainty of a possible pain generator in chronic axial pain illness, it is necessary to view the aforementioned confounding factors for contribution to the illness behavior observed (Table 16–2). An injured soldier with facial trauma, after narcotic administration and in the heat of combat, may mask the perception of a significant low back pain injury, which otherwise could be clearly symptomatic. In this case, a bona fide local pain generator results in little pain perception. Conversely, a very minor nociceptive input (common backache) from a disc can be amplified in the case of a patient with multiple chronic pain syndromes, narcotic habituation, depression, and compensation issues (social disincentives). In this case, a common mild backache pain generator is amplified to become a catastrophic illness.

TABLE 16–2 Neurophysiologic Factors Influencing Result of Diagnostic Injections

Modulator of Diagnostic Injection Effect	Type of Effect on Pain Perception at Site of Injection	Diagnostic Effect
Adjacent tissue injury	Increased regional pain perception	Decreased specificity in provocative injection
Local anesthetic	Decreased pain perception at depot site and sometimes in sclerotomal or referral pattern	Decreased specificity in provocative injection
Tissue injury in adjacent or same sclerotome	Increased regional pain perception	Decreased specificity in provocative injection
Chronic pain syndrome	Increased generalized pain perception	Decreased specificity in provocative injection
Narcotic analgesia	Decreased generalized pain perception and affective response	Decreased sensitivity and increased specificity of provocative injections
Narcotic habituation	Increased pain perception and exaggerated affective response	Decreased specificity in provocative injection
Depression, anxiety, and somatic distress	Decreased generalized pain perception and unpredictable affective response	Decreased specificity in provocative injection
Social imperatives	Decreased pain perception, suppressed affective response	Decreased sensitivity and increased specificity of provocative injections
Social disincentives	Specific increased pain reporting and demonstration of pain behavior	Decreased specificity in provocative injection