What is the role of botulinum toxin in the treatment of muscle spindle-related conditions?

Updated: Mar 11, 2019
  • Author: Heather Rachel Davids, MD; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Little evidence exists that painful muscle areas, such as TrPs, are associated with structural change or sensory structures, such as the muscle spindle; however, the spindle is intimately involved in certain conditions of abnormal muscle activity. In the spastic condition, for example, the stretch reflex is enhanced for a variety of reasons, such as lack of inhibition from spinal cord interneurons. Whatever the reason, muscle spindle physiology is an important regulator of muscle tone in the spastic condition.

BoNT-A has been recognized to reduce pain associated with various clinical conditions, including craniocervical dystonia, tension headaches, cervicogenic headaches, and migraine, an effect that has been observed independently of the toxin's effect on muscle relaxation. (As stated above, however, controversy exists regarding botulinum toxin's effectiveness in the treatment of headache.) [27, 29, 34, 35, 36, 37, 38]

Importantly, BoNT-A has been shown to inhibit release of neurotransmitters involved in pain transmission, including glutamate and substance P in rats. A formalin-induced pain model in rats has helped to show that a local peripheral injection of BoNT-A can significantly reduce glutamate release, signs of pain, and local edema without inducing muscle weakness. These preclinical observations have yet to be definitively confirmed in human patients; however, they provide a possible rationale for BoNT-A's use in chronic painful conditions, including chronic myofascial pain syndromes.

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