Titration of Phenol Nerve Block Effects on Peripheral Nerves: Electrophysiologic and Mechanical Measurements

OBJECTIVE: The purpose of this study was to titrate the nerve block effect of phenol with different concentrations of phenol solution by electrophysiological and mechanical measurements. METHOD: Right tibial nerves of twenty three adult rabbits were blocked by phenol solution with different concentrations (3%, 5%). Nerve conduction study for compound muscle action potential (CMAP), tension by electrical stimulation, and stiffness (slope) of stretch reflex of the triceps surae were performed after nerve block (4 weeks, 8 weeks, 16 weeks). The ratios of each values of right limb to those of left limb were used to evaluate the nerve block effect. RESULTS: The ratios of CMAP amplitude, tension, and slope of 3% group were 0.36, 0.55, and 0.56 at 4 weeks and those of 5% group were 0.21, 0.25, and 0.58. There were statistically significant differences of the CMAP amplitude and tension ratios, however there was no statistically significant difference of the slope ratio between two groups at 4 weeks. The ratios of CMAP amplitude, tension, and slope of 5% phenol group were increased with time. CONCLUSION: Nerve block effects by 5% phenol solution were greater than 3%. These data suggest that nerve block effect can be titrated with concentration of phenol solution.

Titration of Phenol Nerve Block Effects on Peripheral Nerves

Chemical neurolysis can be an extremely effective intervention for reducing spasticity. Phenol nerve block as a method of chemical neurolysis has been used over 40 years, nevertheless, many clinicians remain reluctant to perform this procedure. This is largely due to the fear of its side effects and complications such as excessive muscle weakness or increased spasticity of antagonistic muscles. The purpose of this study was to titrate the nerve block effects of phenol with different concentrations and different volumes of the phenol solution. Left tibial nerves of forty eight adult rabbits were injected with phenol solution of different concentrations(5%, 4%, 3%) and volumes(0.3 ml, 0.2 ml, 0.1 ml) into the epineural sheath. Nerve conduction study of the gastrocnemius muscle was performed before and after the nerve blocks(1day, 1week, 2weeks, 4weeks, 8weeks). The proportion of compound muscle action potential(CMAP) amplitudes and areas before and after the nerve blocks was used for the evaluation of nerve block effect. There was a statistically significant difference in the proportion among three volumes of phenol solution(p0.05) although the higher concentration of phenol solution showed the tendency for smaller proportion. The area of histological degeneration appeared at 2 weeks following nerve block alongside the perineurium. The depth of degeneration area of nerve fascicle varied according to the distance from injection point. These data suggest that the nerve block effect of phenol can be titrated more easily with the volume of phenol solution rather than the concentration until 8 weeks after the nerve block. The variation of the extent of degeneration with different volumes of phenol solution seems to be the mechanism for the titration.