The Use of Botulinum Toxin in Parkinson's Disease
by Michael Rezak, MD, PhD
Botulinum toxin is the most potent biological toxin known to exist. Fortunately, science has harnessed its potential and made it available to treat a number of troublesome disorders. Currently, there are two serotypes of botulinum toxin that are FDA approved for human use, Botox® (Botulinum toxin type A) and Myobloc® (Botulinum toxin type B). Botulinum toxin blocks the release of acetylcholine at the neuromuscular junction, thus effectively cutting off the messages originating in the brain, carried by the nerves to the muscle.
Although the underlying neuropathology is similar in older age onset and young onset PD (YOPD), YOPD can be differentiated by several unique features. These include the tendency to manifest a greater likelihood of developing motor fluctuations and dyskinesias related to the use of levodopa as well as a greater likelihood of developing dystonia of a limb (usually the foot) when in the "off" condition ("off dystonia").
Dystonia is a condition that can be defined as a contraction of a muscle or group of muscles that often results in an abnormal position of the body part that is involved and it can be quite painful. The muscle contractions can be continuous or intermittent. Dystonia can be seen as an independent illness or as a part of other neurological disorders. It is very common in YOPD to experience foot or hand dystonia first thing in the morning before taking medications (as an "off" phenomenon). Once the medicines begin to act, the contractions resolve. Sometimes the dystonic contractions will reoccur when a dose of medicine is wearing off or if a dose of medicine is insufficient to achieve therapeutic value. Occasionally, the dystonia may be continuous and last throughout the day. It should be noted that dystonic contractions can also occur as levodopa related side effect, typically as a peak dose dyskinesia. Botulinum toxin to treat dystonia in YOPD is very effective. Most often Botox® is used and is injected into the dystonic muscles which are accurately identified with the use of a hypodermic EMG needle and EMG guidance. By blocking the messaging going to these muscles one is effectively weakening them thus allowing muscles that may have been persistently contracted to return to a more normal (and easily movable) state. Because of its limited duration of action, Botox® will need to be reinjected every 3-4 months.
Another common condition seen in PD is sialorrhea (drooling). Drooling in PD is typically a result of bradykinesia and rigidity of the oral and pharyngeal muscles resulting in slowed swallowing of saliva which is otherwise manufactured at a normal rate. Drooling is not only an annoyance, but can result in significant embarrassment and social isolation. Excellent results have been obtained by injections of botulinum toxin into the salivary glands reducing the production of saliva by 30-50%. Botulinum toxin has also been reported to be helpful in treating tremor, constipation, and bladder difficulties in PD.
A great advantage of using botulinum toxin for the treatment of the conditions noted above is that it is discrete, i.e. it only impacts the areas into which it is injected as opposed to oral medications which have a more widespread effect (and thus more potential for side effects).
Furthermore, the efficacy of botulinum toxin for dystonia and sialorrhea has been well established with a low side effect profile when used by an experienced practitioner. There is minimal discomfort and the benefits typically last for 3 to 4 months. The major risk in using botulinum toxin is that of excessively weakening muscles or unintentional weakening of muscles. For example, when using botulinum toxin in the neck region swallowing difficulties can be a side effect. As noted above, consulting a physician experienced in using botulinum toxin will minimize the risks. In some cases, the use of Botox® to treat dystonia is covered by insurance including Medicare and Medicaid. Contacting your insurance provider to determine coverage or obtain pre-approval is advisable.
There is no doubt that botulinum toxin has been revolutionary allowing us to treat many difficult conditions that could not be adequately treated with oral medications.
Dr. Rezak is the Medical Director of the APDA National Young Onset Center as well as the Director of the Movement Disorders Center and Co-Director of the Deep Brain Stimulation Program of the Neurosciences Institute at Central DuPage Hospital in Winfield, IL. Dr. Rezak is also on the Speaker's Bureau for Allergan, Novartis, Medtronic, Teva, and GlaxoSmithKline.