Botox (onabotulinumtoxinA) is a prescription injection 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 can also be used to treat jaw spasms, excessive saliva production (sialorrhea), and difficulties with swallowing (dysphagia), all of which can cause uncontrolled drooling in people with spinal muscular atrophy (SMA).
However, it is important to note that 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 neurological disorders. The use of Botox in patients with SMA is experimental, and patients should consult with a physician before considering Botox.
How does Botox work?
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 chemical that relays the nerve signal at that junction is acetylcholine. Once released by nerve cells, it binds to receptors found on the surface of muscle cells, signaling them to contract. An enzyme then degrades acetylcholine, resetting the neuromuscular junction so it is ready for the next nerve signal.
Botox contains a toxin isolated from a bacterium called Clostridium botulinum, which blocks the transmission of nerve signals by preventing the release of acetylcholine from nerve cells. Botox acts locally (where it is injected), and prevents muscle contractions.
Botox research for SMA
Botox can be used to reduce muscle stiffness, a common problem in people with SMA, by allowing muscles to relax. It can also be used to reduce nerve signals to the muscles of the jaw and throat, which can cause problems with swallowing.
A case study published in the journal Brain & Development described a 21-year-old with SMA type 2 and severe 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 difficulty. They successfully added his dysphagia by injecting the muscle in question with Botox, which relaxed the muscle and prevented further spasms. Following treatment, the man reported a marked reduction in the frequency of choking during meals. The study was conducted at the Ehime University Graduate School of Medicine in Japan.
Another case study on 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. Prior to injection, these young people had excessive salivation, which would require frequent mouth-wiping but could also lead to aspiration pneumonia. Injections were made by physicians experienced at Botox injections and guided by ultrasound into the salivary glands at tertiary hospitals in the greater New York area.
After injections, parents of the patients (three infants and a 15-year-old boy) completed surveys to measure their drooling, which included the number of bib changes and mouth wipes before injection, and then four to six weeks after injection. All reported a significant reduction in drooling with no adverse side effects associated with the injection. The risk of side effects was lessened by using minimal dosages and volumes for each gland, and ultrasound guidance to helped ensure the injection was to the middle of the gland, maximizing the distance the toxin would have to spread before reaching musculature. Electrical stimulation was also used to avoid the facial nerves.
A retrospective study assessed the effect of a Botox injection in 13 children with neurological disorders and sialorrhea, including one boy with SMA type 1. All had a history of hospital visits due to respiratory distress, believed caused by drooling and aspiration pneumonia. Injections were made using ultrasound guidance at the Oishei Children’s Hospital of Buffalo, New York. After the injection, the 13 patients had fewer hospital admissions or days spent in the hospital, a drop in antibiotic use, and a lesser need of chest X-rays.
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 that require immediate medical attention.
Last updated: Feb. 18, 2020
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