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The Diagnostic Value of Discography.

The use of discography in diagnosing degenerative disc disease has been a subject of debate among many in the radiologic sciences. Discography is one of the most controversial diagnostic spinal injection procedures available today.[1] The controversy over discography pertains to its accuracy, specificity and the complications associated with this invasive technique.[2] What is discography, and does it have any value in diagnosing pathology of the spine? Have MR and CT scanning limited the need for discograms?

Discography, which means "study of the disc," is an invasive diagnostic procedure used to determine the condition of the spinal discs in either the cervical, thoracic or lumbar regions of the spine. This technique links the patient's symptoms and pain with the abnormality of a certain disc. Discography often is used as a last resort in the diagnosis of spinal pain after exhausting all other techniques and studies, such as MR and CT.[1]

The procedure is performed in a sterile environment, usually in the special procedures room, which allows for fluoroscopic guidance of the needle for injection. The needle is inserted through the skin into the nucleus pulposus of various intervertebral discs. Once the location of the needle is verified with a fluoroscope, a small amount of water-soluble contrast media is injected into the disc. The patient is monitored closely during the injection procedure and is asked to rate his or her sensation of pain or discomfort on a scale of 0 (no sensation) to 10 (extreme pain or pressure) and state whether the pain is equivalent to the pain they experience on a daily basis.[3]

The discogram often is followed up with a CT scan, especially after findings of an abnormal disc. This is referred to as CT/discography or CTD. CTD offers more distinct and accurate representations of disc herniations than discography alone. CTD also provides radiologists with better documentation of minute changes in the pathoanatomy of the disc.[4]

CT scanning and MR studies, when used individually, are limited to determining whether there are abnormalities in a particular disc.[1] The images produced by these techniques cannot be used to conclude whether the abnormal disc is responsible for the patient's pain or discomfort. The deteriorated disc may not be the cause of pain but may be a sign of benign degenerative changes.[2] However, MR is essential prior to a discogram procedure because it helps determine which levels of the spine are suspect and should be injected with contrast should a discogram be necessary.[1]

The provocation of pain in the disc is the most important aspect of discography.[1] When the disc in question has an annular disruption or tear, pain is stimulated during the injection of the contrast media. To relieve the pain, the disc is then injected with a local anesthetic. These events, along with subsequent radiographs, lead to the conclusion that the disc is abnormal and is responsible for the patient's pain. On the other hand, when a normal disc is injected with the appropriate amount of contrast the patient should feel only a slight pressure sensation in the area.[1]

The use of discography in determining which levels of the spine are responsible for the patient's symptoms is crucial for a successful diagnosis and treatment with surgery.[2] Discograms give important preoperative information that helps establish what particular fusion procedure should be performed.[1] The surgical outcome, expressed in terms of clinical benefit to the patient, has been shown to improve significantly when surgery follows a positive discogram vs a nonsymptomatic or negative discogram.[2] Patients should consider discography only if they are considering and are able to proceed with surgery following a positive discogram.

Certain factors should be examined before performing this invasive procedure on a patient, because complications may occur.[1] Contraindications include severe allergy to contrast media, bleeding diathesis and uncontrolled infection in the body. Another factor that could exclude a patient from the procedure is spinal cord compression. Enlargement of the disc with contrast during the procedure could cause further cord compression.[5]

Possible complications of discography include discitis, bleeding, allergic reaction to the contrast, nerve root irritation and a temporary increase in the patient's pain. The use of antibiotics during discography has been shown to reduce the risk of discitis, the most serious complication other than a contrast reaction.[1] In one study, a patient developed quadriplegia after suffering discitis.[5]

In a recent study published in the Journal of Spinal Disorders, four complications were reported.[5] The study included the injection of 269 cervical discs during 161 procedures. The complication rate was 2.48% for the total number of procedures and 1.49% for the total number of cervical discs injected. The complications included 2 cases of discitis, 1 case of postinjection hematoma and 1 case of severe headache pain. The cases of discitis were the only complications considered serious and both patients went on to a spontaneous fusion at the affected level. All 4 patients improved with treatment.

There also is a link between the number of procedures performed by a facility and the rate of complications. Facilities that performed an average of 3 discograms per month reported a much lower complication rate than facilities that performed less than 1 procedure per month. Thus, the experience of the facility and the discographer affect the safety of the procedure.[5]

One of the major reasons for the debate over the accuracy and specificity of discography relates to the fact that patients' response to painful stimuli is an important part of the procedure and diagnosis. At least 1 level or disc that is shown to be negative prior to the discogram should be tested to record the patient's reaction. If there is a painful response to a seemingly normal disc, then the patient's reaction to an abnormal disc may not be accurate. The accuracy also is suspect if a seemingly abnormal disc provokes no pain response by the patient. It is possible that the patient's pain response may be due to his or her sensitivity to the procedure itself.[1]

Although MR and CT scanning are capable of diagnosing degenerative disc disease, they are unable to correlate these findings with the patient's symptoms and this establishes the need for discograms. Discography is a diagnostic tool that provides valuable information about the source of a patient's pain, but it should be considered only if degenerative changes were apparent on previous studies and if surgery is an acceptable treatment. It is apparent that discograms may be performed safely and with few serious complications by experienced and skilled physicians in facilities that offer adequate imaging equipment. The debate over the safety and reliability of discography is sure to continue until further thorough scientific studies are completed.

References

[1.] Kinard RE. Diagnostic spinal injection procedure. Neurosurg Clin North Am. 1996:151-165.

[2.] Daftari TK, Horton WC. Which disc as visualized by magnetic resonance imaging is actually a source of pain? Spine. 1992:S164-S171.

[3.] Dorwart RH, Pollei SR, Schellhas KP. Thoracic discography: a safe and reliable technique. Spine. 1994:2103-2109.

[4.] Muro T, Ninomiya M. Pathoanatomy of lumbar disc herniation as demonstrated by computed tomography/discography. Spine. 1992:1316-1322.

[5.] Guyer RD. Complication of cervical discography: findings in a large series. J Spine Disord. 1997:95-101.

Tami L. Juntura is a senior student at the Clark F. Miller School of Radiologic Technology at Central Maine Medical Center in Lewiston, Maine.

Cynthia Daniels, B.S., R.T.(R), is editor of this section of the Journal, dedicated to publishing the written works of students in radiologic science educational programs. Ms. Daniels is chairman of the ASRT Committee on Student Writing Competitions. She is coordinator of the radiography program at Barnes Jewish Hospital in St. Louis, Mo.

Articles published in the "Student Scope" column are eligible to compete for the Mallinckrodt-Radiologic Technology Writing Award. Writing guidelines may be obtained by contacting Dana Bigbie, c/o the American Society of Radiologic Technologists, 15000 Central Ave. SE, Albuquerque, NM 87123-3917.
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Author:Juntura, Tami L.; Daniels, Cynthia
Publication:Radiologic Technology
Date:Nov 1, 1998
Words:1335
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