Botulinum toxin has an increased effect when targeted toward the muscle's endplate zone: A high-density surface EMG guided study

Objectives: To compare the effect of endplate-targeted injections of a low Botulinum neurotoxin type A (BoNT-A) dose with that of injections at defined distances from the motor endplate zone. Methods: In eight healthy volunteers, the main endplate zones of the right and left extensor digitorum brevis (EDB) muscles were localized using high-density surface EMG. On the study side BoNT-A was injected at fixed distances from the endplate zone. On the control side, BoNT-A was administered into the endplate zone. Compound muscle action potential (CMAP) prior to the injection and 2, 12, and 24 weeks later were recorded. Results: On the control side, the mean CMAP reduction 2 weeks after BoNT-A injection was 79.3%. The difference in CMAP reduction between both EDB muscles was significantly related to the injection distance from the endplate zone. Increasing the injection distance by 1 cm reduced the effect of BoNT-A by 46%. Conclusions: Guided injection of a reduced BoNT-A dose into the muscle's endplate zone(s) is a promising strategy for optimizing the therapeutic effectiveness of BoNT-A and for minimizing side-effects such as unwanted weakness of adjacent muscles. Significance: Precise endplate-targeted injections increase the effect of BoNT-A and may thus prove to reduce required dosage and treatment costs. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.