What is the role of BoNT-A in the treatment of spasticity?

Updated: Mar 01, 2018
  • Author: Krupa Pandey, MD; Chief Editor: Stephen A Berman, MD, PhD, MBA  more...
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Answer

BoNT-A injections have been used as a safe and effective treatment for a variety of movement disorders, including muscle overactivity and spasticity. BoNT-A therapy is approved by the FDA for the treatment of cervical dystonia, primary axillary hyperhidrosis, strabismus, and blepharospasm in patients older than 12 years. The use of BoNT-A to treat spasticity in adults and children is therefore off-label. Controlled clinical trials of BoNT-A injections for focal muscle spasticity have demonstrated prolonged, yet reversible, clinical effects; few adverse effects; and minimal immunogenicity. [29, 30]

BoNT-A inhibits acetylcholine release at the neuromuscular junction. Once inside the cholinergic nerve terminal cell, BoNT-A inhibits the docking and fusion of acetylcholine vesicles at the presynaptic membrane. The effect of the toxin becomes evident within 12 hours to 7 days, and the duration of effect is usually 3-4 months but can be longer or shorter. Gradually, muscle function returns by the regeneration or sprouting of blocked nerves forming new neuromuscular junctions.

In pediatric patients, treatment should be initiated at a time when children still are developing their motor control apparatus. This may prevent them from entering a vicious cycle in which central nervous system (CNS) lesions affect the musculoskeletal system, thereby preventing the development of motor functions. In addition, experimental data on the formation of a cortical somatotopic map during early life indicate that the periphery plays an instructional role on the formation of central neuronal structures.

Proficiency in dosing and injecting BoNT-A demands the development of considerable skill. Each patient's treatment must be individualized, and appropriate patient selection is important. BoNT-A injections are most effective in relieving focal spasticity around a joint or series of joints.


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