This technique is used to diagnose discogenic pain, pain generated from the intervertebral disc. This technique is properly termed provocation or discography as the disc is stimulated in an attempt to reproduce clinical pain. This study attempts to reproduce internal disc pressures, similar to pressures generated in painful activities, in order to diagnose disc pain. A normal disc accepts the injection of contrast without pain, usually maintains a high internal pressure with the injection, and demonstrates no leak of contrast from the central portion of the disc.
The injection of an abnormal disc will cause pain similar to the patient's symptoms at a relatively low internal pressure, and may demonstrate an abnormal pattern of contrast spread. A CT obtained immediately after the discogram will delineate the internal anatomy of the disc. Therefore, discography, when performed correctly and according to protocol, can generate information about pain physiology as well as internal disc anatomy. The patient is placed on the fluoroscopy table in the prone position. An antibiotic is administered intravenously to help prevent infection. After sterile preparation of the back, the needles are carefully placed in the center of each disc to be tested. It is important to place these needles atraumatically in order to obtain optimal interpretation of the procedure.
The patient needs to be calm and relaxed in order to concentrate on the sensations associated with the injection and to accurately describe these sensations to the discographer. Because of this active participation, it is important that the patient be awake and minimal sedation is used. After the needles are in position, the patient is asked to describe the sensation experienced with each injection. Each needle is injected with one to three ml of a contrast-antibiotic mixture while internal disc pressures are measured, the pattern of contrast spread is observed and recorded, and the patient's perception of pain is documented.
Disc stimulation has been well studied in the lumbar spine. Less is known about the cervical discs. In the cervical spine, analgesic discography is sometimes used to diagnose the area of pain. In this procedure, a needle is placed through the anterior neck into the appropriate cervical disc. Contrast mixed with local anesthetic is injected. The patient is tested for a decrease in pain and a CT scan is usually ordered. Disc stimulation is not a therapeutic technique. It is designed to make a diagnosis. The consequences of positive discography may include major surgery or other interventions and, therefore, it is imperative that this procedure be performed with the utmost attention to detail.
Several studies have demonstrated the inaccuracy of this procedure if performed on patients without appropriate pain or with psychological illness. Therefore, logic dictates that disc stimulation should only be performed on patients who have clinical pain consistent with disc pathology and who have no psychological disease.