At times, MRI scans can show tears in the outer wall of the disc, called high intensity zones (HIZ). This may indicate a greater potential of a pain sensitized disc. Many studies have shown the presence of irritating chemical substances within the outer wall of the disc that could cause sensitization of the disc to mechanical weight bearing. It has been demonstrated that nerves supplying the outer disc wall can grow into disc tears or areas of injury causing the disc to become sensitive and painful.
The discogram procedure begins when the skin is anesthetized using a local anesthetic such as Novocain or Lidocaine. A needle introducer is advanced under x-ray guidance into the center of the disc. A solution of dye is injected very slowly into the disc and pressures are measured. During the injection phase the patient is asked to inform the doctor of any discomfort. Several of the discs are usually tested, including one disc that appears to be normal that is used as a control, or comparison level. It is anticipated the patient will not be aware of any feeling when the dye is injected into a normal disc.
If the disc is abnormal the patient will begin to feel some discomfort. Based on the patient's response and the internal pressure of the disc recorded during the procedure, a diagnosis can be made. Once discomfort is felt, the test of that disc is stopped. The concept is to identify an abnormal disc, not to measure pain tolerance. After a brief time of observation, the patient is released from the center. The procedure is considered minimally invasive and done on an out-patient basis. In patients with dye allergies, saline can be substituted for the dye.