The long-term effect of chemonucleolysis on the intervertebral disc as assessed by magnetic resonance imaging.

With Magnetic Resonance Imaging (MRI) it is possible to monitor the changes in water content of the nucleus pulposus after intradiscal injection of chymopapain. In this prospective study the changes that occurred in 20 patients undergoing single-level chemonucleolysis were monitored. A constant pattern of gradual reduction of nuclear signal was seen in all cases. Complete loss of signal took at least 6 weeks and corresponded to the maximum reduction in disc space height. Seventeen patients were scanned at more than 1 year after treatment. Of these, 13 had been treated by chemonucleolysis alone. No significant return of signal from the nucleus pulposus was noted despite a slight reconstitution in disc space height. Chymopapain produced irreversible changes analogous to gross premature disc degeneration. No similar changes were noted in a control group of 12 patients (31 discs) undergoing diagnostic discography without injection of the enzyme.