Phenol reduces hypertonia and enhances strength: a longitudinal case study.

Phenyl alcohol blocks are used to relieve spasticity. Such nerve conduction blocks result from phenol-induced axonotmesis and could potentially affect muscle properties related to the ability to generate, maximize, and reduce force. This study assessed the 12-week longitudinal effect of phenol on position (stiffness) and velocity (damping) components of hypertonia, in addition to strength (peak torque and times to generate and reduce torque) in an individual with chronic elbow flexor spasticity following stroke. Phenol motor point injections of flexor muscles paradoxically increased the magnitude of flexion torque and decreased the times required to generate and reduce flexion and extension joint torques, in addition to reducing elbow extension stiffness and damping. Large reductions in the velocity-related component of hypertonia (damping changes > 90%) occurred immediately following injection, which is a finding that supports the velocity-dependent definition of spasticity. Although the changes in damping were large and transient, changes in stiffness and strength variables were small, slower to occur, and maintained. This suggests secondary changes following nerve block, possibly facilitated by regular elbow use subsequent to spasticity reduction.