Spasticity is a major clinical problem that causes incoordination, pain and joint contractures, in patients with upper motor neuron disease. But the ideal means of management of spasticity is not yet available. Phenol injections of peripheral nerves have been used to reduce muscle tone temporarily.

The attempt of this study was to determine the development of degeneration and the process of regeneration of open phenol injection of the sciatic nerves of rats. The sciatic nerves of the Wistar rats were surgically exposed and injected with 0.9% normal saline in the right as control and 5% aqueous phenol in the left, and then examined at various intervals until 24 weeks by the electrophysiologic study and the light and electron microscope.

The results were as follows:

1) The was no difference of the distal latencies of CMAPs between and after phenol injection. There were marked decrements in amplitudes after 24 hours and some increments after 1 week but these were not reached the value prior to injection until 24 weeks.

2) The needle EMG study showed abnormal spontaneous activities after 1 week, most profuse in 2 weeks after block, and not any longer after 8 weeks of phenol injection. Immediately after phenol injection there was no motor unit action potentials until 24 hours but a few polyphasic potentials were noted in a week. Nearly full recruitment pattern was shown in 16 weeks.

3) Histologic studies showed severe degenerative changes in both myelinated and unmyelinated nerve fibers 30 minutes after phenol injection. Regeneration of some unmyelinated axons was found in 2 weeks and that of myelinated axons in 4 weeks. In 8 weeks there was an increased number of regenerated axons but still less than after saline injection. A few scattered degenerated nerve fibers and the increase in collagen were observed even after 24 weeks.