Related Experiment Video
Updated: Nov 17, 2025

Behavioral Characterization of Pentylenetetrazole-induced Seizures: Moving Beyond the Racine Scale
Published on: July 8, 2025
The Time Course of Onset and Peak Effects of Phenol Neurolysis
Bei Zhang1, Nathan Darji, Gerard E Francisco
1From the Department of Physical Medicine and Rehabilitation, McGovern Medical School University of Texas Health Science Center-Houston, Texas (BZ, GEF, SL); TIRR Memorial Hermann Hospital, Houston, Texas (BZ, ND, GEF, SL); and H. Ben Taub Department of Physical Medicine and Rehabilitation, Baylor College of Medicine, Houston, Texas (ND).
Objective:
The aim of this study was to explore the time course of onset and peak effects of phenol neurolysis.
Design:
This is a retrospective chart review. Eleven patients with elbow flexor spasticity after brain injury were enrolled. The resting angle of the elbow joint was measured before and after the injection and up to 6 wks of follow-up.
Results:
Phenol injection was performed to 13 musculocutaneous nerves under ultrasound and electrical stimulation guidance. The resting elbow angles were 84.4° ± 25.8° (before injection), 116.6° ± 20.9° (immediately after injection), 121.2° ± 21.4° (2 hrs after injection), 127.2° ± 19.7° (24 hrs after injection), 145.4° ± 11.8° (7 days after injection), 145.5° ± 10.4° (14 days after injection), and 150.3° ± 12.2° (6 wks after injection; N = 7). The mean resting angle was statistically different among the time points from preinjection to 14 days after (F2.625, 31.505 = 36.805, P < 0.01). Post hoc tests revealed that significant improvements existed immediately after and 7 days after the injection (P < 0.01 for both). The effects seemed to reach its peak in 7 days. The effect sizes immediately and 7 days after the injection were 1.37 and 3.04, respectively. The immediate effect accounted for approximately 60% of the maximal effect.
Conclusions:
Phenol neurolysis has an immediate effect on spasticity reduction and reaches its peak effect around 1 wk after injection.
Related Concept Videos
Local Anesthetics: Adverse Effects
Once absorbed into the systemic circulation, local anesthetics can affect the organs that depend on the functioning of sodium...
Local Anesthetics: Pharmacokinetics
Local Anesthetics: Differential Sensitivity of Nerve Fibers
Local Anesthetics: Chemistry and Structure-Activity Relationship
Depolarizing Blockers: Pharmocokinetics
Long-term Potentiation

