Effect of arachnoiditis on pain threshold.

A model for studying the relationship between chronic arachnoiditis and pain sensitivity was developed. Thirty male ICR mice were randomly divided into three groups and the tail-flick test was done using an EMDIE-TF6 apparatus (Emdie Instrument Co., Montpelier, VA). Ten mice were injected intrathecally with 5.0 microL of a kaolin-metrizamide mixture and ten control mice were injected intrathecally with 5.0 microL of an electrolyte solution resembling CSF. A third group, (naive controls) were given no treatment. Six weeks later tail-flick tests were repeated. The kaolin-treated mice had significantly decreased tail-flick latencies (P less than .05) compared with the baseline; the controls had no significant change in tail-flick latency. Histologic examination revealed moderate to severe arachnoiditis in the kaolin-treated animals and no evidence of arachnoid abnormalities in the controls. This study suggests that arachnoiditis may be associated with decreased pain thresholds.