Intraspinal alumina injection: the relationship between epileptiform focus, root scarring and chronic pain

Intramedullary or subarachnoid injections of alumina cream were made in the lumbar region of 38 adult cats. The animals were observed for 3 to 12 months and then subjected to acute neurophysiologic and histologic analysis. Neuronal hyperactivity in the dorsal horns was reliably produced by either subarachnoid or intramedullary alumina; behavioral abnormalities were not produced unless some of the alumina was present adjacent to dorsal root fibers in the subarachnoid space. Neuronal hyperactivity does not predict cutaneous hyperesthesia or motor abnormality; alumina produces scarring in the subarachnoid space and probably causes pain by making the dorsal root fibers mechanosensitive. Subarachnoid alumina may be a good model for human arachnoiditis.