Successful treatment of painful traumatic mononeuropathy with carbamazepine: insights into a possible molecular pain mechanism.

The delayed onset of painful paresthesias following trauma to a peripheral nerve is a well recognized but poorly understood phenomenon. This report describes an illustrative case of painful paresthesias in the territory of the ilioinguinal nerve, 3 to 6 weeks after an otherwise routine herniorraphy, which subsequently responded dramatically to carbamazepine. The case is considered in light of recent studies which have determined molecular changes which occur in dorsal root ganglion (DRG) neurons following axotomy and neuroma formation. Voltage-dependent sodium (Na+) channels in DRG neurons undergo a change following axotomy, in which there is significant up- and down-regulation of different subpopulations of Na channels over a time frame measured in days to weeks. Such changes may render the DRG neurons hyperexcitable, thus contributing to a neuropathic pain syndrome, yet susceptible to treatment with a sodium channel blocker such as carbamazepine.