Effect of chymopapain on the meninges studied in an experimental model

The effect of chymopapain and contrast media in the epidural space on meninges has not been studied conclusively. The authors injected chymopapain into the epidural space of monkeys and measured the degree of arachnoid fibrosis that resulted. Animals were given injections of 1.2 mL of diatrizoate (280 mg iodine per milliliter), chymopapain (100 IU/mL), kaolin (100 mg/mL) (as a positive control), or saline (0.9%) (as a negative control). Three months later the animals were killed; the dural sac was removed intact and was fixed, sectioned, stained, and examined with light microscopy. Kaolin-treated animals developed mild to marked fibrosis of the dura. The saline- and diatrizoate-treated animals developed little or no evidence of fibrosis. One of four chymopapain-treated animals developed degenerative changes in dorsal nerve roots and fibrosis in the adjacent arachnoid. The other chymopapain-treated animals had little or no evidence of fibrosis. The studies suggest that neither diatrizoate nor chymopapain causes arachnoid fibrosis.