Botulinum toxin injections can provide substantial improvement of dystonic symptoms, especially in the focal dystonias. It is a therapeutic muscle-relaxing agent that helps reduce the involuntary contractions characteristic of dystonia. It is injected into specific muscles where it acts to relax the muscles and reduce excessive muscle contractions.
Botulinum toxin is derived from the bacterium Closridium 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 or eliminated.
Forms of botulinum toxin
Two forms of botulinum toxin are available for patients. These are botulinum type A(trade names Botox, Dysport, and Xeomin) and botulinum toxin type B (trade names Myobloc and Neurobloc ).
Other ‘ serotypes’ of botulinum toxin are under investigation as therapeutic agents. These include (in addition to types A and B) 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 has shown 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 injection while pregnant.
Injections of botulinum toxin should only be performed by a doctor who is trained to administer this treatment. The doctor needs to know the clinical features and study the involuntary movements of the person being treated. The doctor 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 the treatment of spasmodic dysphonia/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 electromyography (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 doctor locate overactive muscles.
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 doctor 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.
An important difference between the different brands of botulinum toxin 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, and the products are not interchangeable.
Like many aspects of treating dystonia, injecting botulinum toxin is as much art as it is science. It is in your best interest to locate the most well trained and experienced doctor you can find.
The success of botulinum toxin injection depends upon:
- The dose used
- The specific sites in the muscles where the product is injected
- The experience of the doctor giving the injection
- Clear communication between doctor and patient, so that both parties understand and agree on the specific symptoms that are been treated and what can be expected as a result of an injection.
Because of the multiple factors that determine the success of botulinum toxin injection, a person might require being injected on two or three separate occasions before the optimal benefit is achieved. All of the factors listed above must be aligned for the best result, and this may take some time to perfect.
Based on over a decade of clinical experience, patients who respond well to botulinum toxin may continue treatment over the course of many years without side effects from long-term use.
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 manufacturing botulinum toxins have been refined to reduce the chances of the body forming antibodies
- Doctors use the smallest dose needed to get a positive result
- Injections are typically not repeated more often than every 3-4 months
- Doctors 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 the 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 adjusted 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 doctor 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 doctor 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, an individual who has previously been successfully treated with botulinum toxin begins to experience a loss of 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.