The introduction of botulinum toxin as a therapeutic tool in the late 1980s revolutionized the treatment of dystonia by offering a new, localized method to significantly relieve symptoms for many people. Botulinum toxin, a biological product, is injected into specific muscles where it acts to relax the muscles and reduce excessive muscle contractions.
Botulinum toxin is derived from the bacterium Clostridium botulinum. It is a nerve "blocker" that binds to the nerves that lead to the muscle and prevents the release of acetylcholine, a neurotransmitter that activates muscle contractions. If the message is blocked, muscle spasms are significantly reduced.
Forms of Botulinum Toxin
In Canada three forms of botulinum toxin is available for patients. This is botulinum toxin type A (trade names Botox®, Xeomin and Dysport).
Two forms of botulinum toxin are available for patients in the United States. These are botulinum toxin type A (trade names Botox®, Xeomin and Dysport®) and botulinum toxin type B (trade names Myobloc® and Neurobloc®).
Other “serotypes” of botulinum toxin are under investigation as potential therapeutic agents. These include (in addition to types A and B) types C, D, E, F, and G. Each one has different properties and actions. No two are exactly alike. At present, type F is the only additional form that is showing some promise as a viable treatment for humans.
Although the overall effect is similar, the specific mechanism by which each serotype achieves this effect is different. For example, both type A and type B block the neurotransmitter acetylcholine, but they do so by breaking up different proteins within the nerve cell.
No studies have been done to examine the effects of botulinum toxin during pregnancy. It is generally recommended that women not receive botulinum toxin injections while pregnant.
Injections of botulinum toxin should only be performed by a physician who is trained to administer this treatment. The physician needs to know the clinical features and study the involuntary movements of the person being treated. The physician doing the treatment may palpate (touch) the muscles carefully, trying to ascertain which muscles are over-contracting and which muscles may be compensating. In some instances, such as in the treatment of laryngeal dystonia, a team approach including other specialists may be required.
For selected areas of the body, and particularly when injecting muscles that are difficult or impossible to palpate, guidance using an electromyograph (EMG) may be necessary. For instance, when injecting the deep muscles of the jaw, neck, or vocal cords, an EMG-guided injection may improve precision since these muscles cannot be readily palpated. An EMG measures and records muscle activity and may help the physician locate overactive muscles.
Injections into the overactive muscle are done with a small needle, with one to three injections per muscle. Discomfort at the site of injections is usually temporary, and a local anesthetic is sometimes be used to minimize any discomfort associated with the injection.
It normally takes several days for the effects of the botulinum toxin to become apparent. The benefit peaks in approximately four weeks and lasts three to four months. Temporary side effects for both types A and B may include muscle weakness, flu-like symptoms, pain at the injection site, and dry mouth. Patients should feel free to ask their physician about additional side effects that may be specific to the body area that is to be injected—for example, temporary difficulty swallowing may occur in patients injected for laryngeal or cervical dystonias, but is highly unlikely for someone getting injected for writer’s cramp. If a patient experiences side effects, adjusting the dosage or site of injection for future treatments may help avoid these effects. There is some evidence that side effects may be more prevalent in people treated with type B.
Note that an important difference between Botox® and Myobloc® is the number of units needed for treatment and how much toxin is in a “unit” of each product. The units used to measure dosage are not consistent among the commercially produced toxins.
Because botulinum toxin is a biological product, it is possible for the body to create antibodies and develop immunity to the effects of the toxin. Measures are in place to guard against immunity:
• The “recipes” for botulinum toxins have been refined to reduce the chances of the body forming antibodies
• Physicians use the smallest dose needed to get a positive result
• Injections are typically not repeated more often than every 3-4 months
• Physicians generally use one serotype at a time rather than alternate or mix type A and type B
An important distinction must be made between individuals who have become immune to the toxin and individuals who have not had an optimal treatment: Someone who has become immune to botulinum toxin does not react at all to the product. This is very different from someone who gets some results from the injections but not the results they were hoping for or expecting. If a person is getting any results at all then there is hope that the way the botulinum toxin is administered can be manipulated to get a good result.
If you are receiving botulinum toxin injections and getting some result but not the result you expected or unacceptable side effects, ask your physician about the specific symptoms that concern you. Treatment with botulinum toxin may require a trial period to establish the appropriate dose, injection sites, and targeted symptoms but it is a very adaptable treatment that can create a dramatic benefit. A physician may test a patient for immunity by injecting a tiny amount of botulinum toxin into the brow muscle and observing the effect.
In some cases, a patient who has previously been successfully treated with botulinum toxin begins to experience a loss in benefit. Several factors could be responsible for this change. The nature and pattern of muscle contractions may change over time, thus necessitating an adjustment in the site of injection and dosage. If deep muscles become involved, it may be difficult to access those muscles. If you notice a change in how your symptoms respond to botulinum toxin, discuss these changes with your doctor.
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