Lumbar discography

Discografia lombar

Lumbar discography

Discografia lombar

Sady Ribeiro^I; Magnolia Leão da Nobrega Gauchée^II

^IPain Specialist, American Pain Board of Medicine, Department of Neurobiology, University of Texas, Houston, USA

^IIDoctor Anesthesiology, Hospital das Clinicas, FMUSP, responsible for Pain Group from Núcleo de Extensão, Casa de AIDS HC, FMUSP, São Paulo, SP

^{Address for correspondence}

SUMMARY

Discography, a controversial test that due to new image diagnosis techniques was left behind, is discussed. A literature review, regarding technique, indications, benefits and limitations of discography is presented. A new approach, focusing the results on presence of a familiar pain during the exam is presented.

Key words: Discography; low back pain; disc herniation

RESUMO

Os autores apresentam uma revisão da discografia, exame controvertido, que com a introdução de novas técnicas , o diagnóstico por imagem, ficou relegado a um segundo plano. Mostram uma revisão da literatura, abordando a técnica, indicações, benefícios, limitações e eventuais complicações deste exame. Uma nova abordagem para o exame com foco na evocação da dor usual, quando a injeção de contraste, é discutida.

Descritores: Discografia; lombalgia; hérnia discal.

Although controversial, discography has been used as diagnostic tool for a half century ⁽²²⁾. When first introduced, the main indication of discography was the assessment of patients with back pain and sciatica, whose myelography, the only test available to study intraspinal pathology at that time, was either negative or indeterminate⁽⁵⁾. The rate of false negatives for myelography, mainly at the level L5-S1, was high⁽¹⁶⁾. Discography proved to be useful for this diagnosis.

Technology gave us the CT and later, the MRI. These two tests significantly improved the diagnosis of back pain with sciatica and made discography a test of secondary value in this clinical circumstance⁽¹⁵⁾.

However, patients with back pain and radicular pain, whether or not accompanied by an abnormal neurological exam, are a minority in the population with back pain.

Axial back pain with or without referred pain (that is different from radicular pain) is the most common presentation in patients suffering from chronic back pain, and to determine the source of pain in this population can be a challenge ⁽⁶⁾.

Our current understanding permits us to consider the disc, independent of any root compression, as the cause of pain in approximately 40% of these patients ⁽²⁶⁾.

The disc presents a neuro-anatomical substrate that gives it a condition of being a pain generator when pathologically altered ⁽⁴⁾. It receives its innervation from branches of the sinuvertebral nerve and the gray rami communicantes. The first supplies mainly the outer annulus of the posterior and posterior lateral aspect of the disc, and the second supplies the lateral and anterior part of it ⁽⁴⁾.

The concept of internal disc disruption introduced in the seventies improved our understanding of intradiscal pathology and how a disc can be a generator of pain. In this condition, fissures occur in the substance of the inner annulus and extend into the outer annulus. A degenerated disc would produce several inflammatogenic substances that, together with mechanical stimuli, could activate the nerve endings of the outer annulus ⁽⁹⁾.

MRI is able to show internal disc morphology. Good quality T2 weighted images provide a contrast between the nucleus pulposus and the outer annulus of a normal disc ⁽⁷⁾. In disc disruptions, eventually, it can be seen in T2 weighted images at the posterior annulus.

This finding has a positive predictive value for a disrupted symptomatic disc of 86% ⁽¹⁾.

However MRI can occasionally miss an abnormal disc, and not all altered discs have been shown to be symptomatic ⁽¹²⁾.

Discography can then be used to determine if one or more discs are responsible for the patient's back pain. Although disc morphology can sometimes be important, in this new use of discography the goal is to reproduce the patient's pain through the injection of contrast or normal saline in the nucleus pulposus ⁽²⁹⁾.

Patients should be interviewed and examined before the procedure. Physicians must explain the nature of the procedure, its goal, and its possible complications. Patients have to clearly understand that the procedure is to search for "every day" pain and not an atypical pain that may appear during the injection⁽¹⁴⁾. Patients should also be instructed about the pain scale (0-10) that will be used to measure the pain. Coagulation function should be tested and corrected when needed.

During the procedure the patient is placed either in the lateral position or prone decubitus position, and connected to an EKG monitor and a pulse oximeter⁽¹⁴⁾. Neuroleptic analgesia is generally administered in order to allow the patient to respond to painful stimuli. The lumbo-sacral area is prepared and draped accordingly.

After the skin and subcutaneous tissue had been anesthetized with lidocaine 1%, a 22-gauge needle is introduced, with the help of fluoroscopy, through an extradural approach in the postero lateral aspect of the disc and placed in the nucleus ⁽²⁸⁾. The position of the needle is assessed by postero ¾anterior and lateral views. The correct positioning of the needle is necessary for the validity of the interpretation of the test ⁽²⁷⁾. Some authors defend the use of a double needle technique, believing that this will decrease the incidence of discitis ⁽²⁵⁾. In this case, an 18-gauge needle is used, and placed just lateral to the annulus; the 22-gauge needle is then passed through it and penetrates into the disc. The placement of the needle at the level L5-S1 can be very difficult due the presence of a high iliac crest, reduction of the height of disc space, an osteophyte or a large transverse process. A needle with a curved tip can sometimes be helpful at this level. Since the most commonly abnormal levels are the L4-L5 and L5-S1, and since it is important to have a normal level as control in order to substantiate the test validity, discography is usually performed in the three lowest levels ⁽⁸⁾. When the L3-L4 level is also abnormal, the level above should be tested. The criteria used to interpret discography include reproduction of familiar pain, volume acceptance, resistance, and morphology of the injected disc ⁽¹⁴⁾. Before the injection the patient is asked to grade his or her pain in a scale of 0 to 10. Contrast is then injected with a three cc syringe. A normal disc has a volume acceptance between 0.5 and 1.5 cc with a firm end point during injection. The injection is not painful and the contrast stays in the nucleus. An abnormal disc is painful; it has a low resistance to the injection, and a volume acceptance that varies with the degree of the degeneration. In an abnormal disc, the contrast spreads to the annulus and can leak into the epidural space. In the presence of pain, the patient is asked again to score it in the 0-10 scale. Although reproduction of familiar pain is the most important parameter, it is common to request a CT after discography for a better documentation of the morphologic changes of the abnormal disc ⁽²¹⁾, mainly when one is considering an intradiscal therapy (laser, chemonucleolysis or automated percutaneous discectomy) ⁽¹¹⁾. It seems that these three procedures present better results with a contained disc. Pain in discography is explained by the presence of a chemical and /or mechanical sensitized nociceptor in the outer annulus. Statistical studies have shown that there is a strong correlation between positive pain response at discography and the presence of a fissure of the outer disc annulus, independently of the degree of disc degeneration ⁽⁷⁾. Hyper flexion of the facet joints and pressure against the vertebral end plate during the contrast injection could also contribute to the pain ^(18,29).

Recently, the use of pressure-controlled discography has been introduced in the practice of this procedure. Using a syringe with a manometer that registers the intadiscal pressure during the injections, we can divide the discs with a positive pain response into two groups. Chemically sensitive discs would present pain with pressure lower than the mechanical sensitive ones . The first group seems to achieve significantly better long-term outcomes with interbody and combined fusion than with intertransverse fusion⁽¹⁰⁾.

Discography has been criticized in the past as a test with high false positive results⁽¹⁷⁾, but studies utilizing a better methodology have demonstrated the validity and reliability of this test⁽²⁷⁾.

A false positive may result from misplacement of the needle either touching the end plate or inserted into the annulus instead of the nucleus⁽²⁹⁾. Patients with a very low pain threshold or psychological problems are perhaps not able to distinguish between pressure due the injection and real pain ⁽³⁾. Clinical correlation and morphologic findings can help us with this scenario. False negatives are very rare and could be caused by an annular tear that does not communicate with the nucleus. Over sedation will also prevent patient from informing the physician about pain. Discography does not injure the disc when properly performed ⁽¹⁹⁾. Complications such as retroperitoneal hemorrhage, intradural injection, and nerve lesion can happen, but are rare in the hands of an experienced physician. With regard to infection, discitis ⁽¹³⁾, although rare, can occur. Epidural abscess has also been described⁽²⁰⁾. Needles should be used with the stiletto and some authors recommend double needle technique to avoid discitis. Antibiotics, given IV and mixed with the contrast, have been used by almost everybody. In experimental models IV cefazolin protected the disk against discitis. When mixed with the contrast, cefazolin is used in a concentration of 1mg/cc. Staphylococcus is the most common bacteria, but when bowel perforation occurs during discography, a gram-negative bacteria can be the aggressor agent. Patients with discitis generally present with a high sedimentation rate and severe back pain. An MRI and bone scan can take from two to four weeks to become positive.

Discography should only be used when is important to define if a disc is symptomatic and there is a specific therapy to be offered. The most common indication is to plan the level of spinal fusion that will include all of the symptomatic discs ⁽²⁰⁾. Patients with abnormal morphologic disc and positive pain seem to present a better outcome to spinal fusion than patients with disrupted morphology, but a negative pain response during disc injection ⁽²³⁾.

In patients with back pain sciatica, CT or MRI must be the first choice, but when these test are inconclusive or intra discal therapy is being considered, discography can be very useful ⁽²⁴⁾. Pseudarthrosis is an important cause of failed spinal fusion, and discography helps in differential diagnosis between a symptomatic pseudarthrosis and a painful disc ^(2,14). Although MRI with contrast usually can differentiate between scar tissue and recurrent hernia, discography with CT has proved to be able to detect recurrent herniation not identified by gadolinium enhanced MRI ⁽²¹⁾. Finally new therapies have appeared for treatment of discogenic pain (IDET, RFTC) and discography is a must in the selection of patients and disc levels that can benefit form these procedures ⁽²¹⁾.

CONCLUSION

Discography certainly is not a perfect test, apart from being an invasive procedure. However when proper used, it can be very helpful in assessing patients with back pain. Correct selection of patients and correlation with patient symptoms and other tests certainly helps us to validate discography results. As the test relies on patient information, those with important psychological problems should not undergo this exam ⁽³⁾. Discography should not be only an intellectual exercise and its overuse will lead to a low acceptance, poor credibility and enraged criticisms.

Magnolia Leão da Nobrega Gauchée E-mail: [e-mail]

Trabalho recebido em 14/12/2001. Aprovado em 22/05/2002

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Publication Dates

• Publication in this collection
  25 Feb 2003
• Date of issue
  Sept 2002

History

• Accepted
  22 May 2002
• Received
  14 Dec 2001