Cervical Dystonia
Safety of Botulinum Toxin Type A
Administration of botulinum toxin type A for the treatment of dystonia
A solution of BTX-A is injected directly into several sites in the overactive, dystonic muscle. These sites are near the nerve terminals or that part of the nerve cell that actually stimulates the muscle to contract. BTX-A works inside the nerve terminals to block the release of the neurotransmitter acetylcholine. This neurotransmitter serves to initiate or elicit muscle contractions. Some nerve terminals remain unaffected by BTX-A; therefore, the injected muscle may still contract but with less force. One important benefit of BTX-A is that the dose may be adjusted to provide the precise degree of weakness needed to overcome dystonia; however, some strength for normal function is preserved.
BTX-A temporarily weakens dystonic muscles, thereby allowing for a more normal posture and function. The benefits that BTX-A conveys to a particular patient depend on the location and relative degree of severity of the dystonic muscles being injected. In general, BTX-A cannot be used alone to treat widespread or extremely severe generalized dystonia, as the drug dose required for this type of treatment would be too high. In these patients, BTX-A may be used to target specific dystonic muscles, thereby improving particular aspects of care and function or relieving discomfort or pain. Many patients with painful muscle spasms report a reduction in pain after injection with BTX-A.
Duration of botulinum toxin type A effect
The effects of treatment with BTX-A are usually greatest for a two- to six- week period following injection. These effects usually fade after about three to six months. If necessary, reinjection of the drug is possible at that time. In order to decrease the possibility of antibody formation, reinjections are usually not administered before three months after the last injection.
Side effects of botulinum toxin type A
During the dose regulation process, physicians work closely with patients to optimize their therapy. Some patients may experience temporary, muscle weakness. This weakness is temporary and wears off. If patients experience muscle weakness, it is important to discuss this finding with their physicians as it may be a signal for a modification of the treatment approach. For example, muscle weakness may be lessened by reducing the dose of BTX-A during the next injection. BTX-A should be used with extreme caution in patients with neuromuscular disease such as myasthenia gravis or amyotrophic lateral sclerosis (ALS or motor neuron disease), or in those who receive therapy with drugs that thin the blood (anticoagulants), or certain antibiotics (aminoglycosides such as gentamicin [Garamycin®], kanamycin [Kantrex®], neomycin [Mycifradin®, Myciguent®, or NeoTab®], streptomycin [Streptomycin], or tobramycin [Tobrex® or Nebcin®]).
The decision to combine injections of BTX-A with other forms of treatment for dystonia is an individual decision and based on many factors. This decision is reached after thorough clinical evaluation and consultation with the treating physician. In some patients receiving injections of BTX-A, the dosage of other medications may be reduced. Certain oral medications as well as baclofen, which may be delivered directly next to the spinal column (intrathecally), may provide global muscle tone reduction, whereas BTX-A injections may provide graded focal relief in selected muscles.
