Changes in contractile properties of muscles receiving repeat injections of botulinum toxin (Botox)

• Published in: Journal of biomechanics 2011-01, Vol.44 (1), p.39-44
• Main Authors: Fortuna, Rafael, Aurélio Vaz, Marco, Rehan Youssef, Aliaa, Longino, David, Herzog, Walter
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Biomechanical Phenomena; Botulinum toxin type A; Botulinum Toxins, Type A - administration & dosage; Botulinum Toxins, Type A - adverse effects; Clinical medicine; Disorders; Female; Foods; Hindlimb; Knee; Medical sciences; Muscle; Muscle Contraction - drug effects; Muscle paralysis; Muscle Strength - drug effects; Muscle weakness; Muscles; Muscular Atrophy - chemically induced; Muscular Atrophy - pathology; Muscular Atrophy - physiopathology; Muscular system; Nervous system (semeiology, syndromes); Nervous system as a whole; Neurology; Personal relationships; Pharmacology. Drug treatments; Physical Medicine and Rehabilitation; Quadriceps Muscle - drug effects; Quadriceps Muscle - pathology; Quadriceps Muscle - physiology; Rabbit; Rabbits; Receiving; Strength; Time Factors; Toxins
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2010.08.020

Abstract Botulinum toxin type A (BTX-A) is a frequently used therapeutic tool to denervate muscles in the treatment of neuromuscular disorders. Although considered safe by the US Food and Drug Administration, BTX-A can produce adverse effects in target and non-target muscles. With an increased use of BTX-A for neuromuscular disorders, the effects of repeat injections of BTX-A on strength, muscle mass and structure need to be known. Therefore, the purpose of this study was to investigate the changes in strength, muscle mass and contractile material in New Zealand White (NZW) rabbits. Twenty NZW rabbits were divided into 4 groups: control and 1, 3 and 6 months of unilateral, repeat injections of BTX-A into the quadriceps femoris. Outcome measures included knee extensor torque, muscle mass and the percentage of contractile material in the quadriceps muscles of the target and non-injected contralateral hindlimbs. Strength in the injected muscles was reduced by 88%, 89% and 95% in the 1, 3 and 6 months BTX-A injected hindlimbs compared to controls. Muscle mass was reduced by 50%, 42% and 31% for the vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM), respectively, at 1 month, by 68%, 51% and 50% at 3 months and by 76%, 44% and 13% at 6 months. The percentage of contractile material was reduced for the 3 and 6 months animals to 80–64%, respectively, and was replaced primarily by fat. Similar, but less pronounced results were also observed for the quadriceps muscles of the contralateral hindlimbs, suggesting that repeat BTX-A injections cause muscle atrophy and loss of contractile tissue in target muscles and also in non-target muscles that are far removed from the injection site.