Botox (onabotulinumtoxinA) is a prescription medication produced by Allergan. It is approved by the U.S. Food and Drug Administration (FDA) to treat urinary incontinence, prevent headaches in patients with chronic migraines, and reduce upper limb spasms. Botox also can be used to treat jaw spasms, excessive saliva production, and the inability to swallow, which can cause drooling in patients with spinal muscular atrophy (SMA).

How Botox works

To move a muscle, a nerve signal is sent from the brain via a nerve impulse to the muscles. This signal starts as an electrical signal and is changed into a chemical signal at the point where the nerve cell meets a muscle cell (the so-called neuromuscular junction). One such chemical is acetylcholine. Once released by the nerve cells it binds to receptors found on the surface of muscle cells, signaling them to contract. An enzyme then degrades acetylcholine, resetting the junction so it is ready for the next nerve signal.

Botox contains a toxin isolated from a bacterium, which blocks the transmission of the nerve signal by preventing the release of acetylcholine from the nerve cells. Botox acts locally (where it is injected) and prevents muscle contraction.

Botox research for SMA

Botox can be used to reduce uncontrollable muscle spasms that SMA patients may experience. It also can be used to reduce nerve signals to the muscles of the jaw and throat that can cause problems with swallowing in people with SMA.

A case study published in the journal Brain & Development described the case of a 21-year old patient with SMA type 2 who had difficulty swallowing. A videofluoroscopic swallow study (VFSS) was performed that allowed physicians to visualize the patient’s throat as he swallowed. They were able to determine that spasming of the muscle, which controls the passage of food and fluids to the stomach, was causing his swallowing difficulty. They successfully treated the patient by injecting the muscle in question with Botox, which paralyzed the muscle and prevented further spasms.

A small case study in four patients with SMA type 1 who received Botox injections into their salivary glands to reduce drooling was published in the American Journal of Physical Medicine & Rehabilitation. Patients completed surveys to measure their drooling, which included the number of bib changes and the number of mouth wipes before injection, and then for four to six weeks after injection. All patients showed a significant reduction in their drooling and there were no adverse side effects.

Other information

Botox is a neurotoxin and can spread to areas outside the injection site, so special care should be taken in patients with SMA or other degenerative neurological disorder. Patients should consult with a physician before using Botox.

Botox can cause minor side effects, including dry mouth, pain or irritation at the injection site, tiredness, and headache. Botox also can cause severe allergic reactions, including rash, welts, and breathing problems.

Following Botox injections to treat muscle spasticity, it is important for patients to work with physiotherapists to safely increase muscle strength and the range of motion they can achieve.


Last updated: 07/11/2019


SMA News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.