Botulinum Toxin

Therapeutic Botulinum Toxin

Botulinum toxin (BTX) has been used at Baylor’s Parkinson’s Disease Center and Movement Disorders Clinic (PDCMDC) in the treatment of dystonia and related disorders since 1983. Its safety and efficacy have been established, partly as a result of the pioneering work at the PDCMDC. Indeed, the first double-blind, placebo-controlled trial of BTX in cranial-cervical dystonia was conducted at Baylor and the findings were used to obtain the initial approval for BTX by the Food and Drug Administration.

Dystonia is a neurological condition manifested by involuntary contractions (spasms) of muscles producing twisting, squeezing or pulling movements and abnormal postures. In addition to dystonias, BTX has been used also to relieve other movement disorders, including hemifacial spasm, tremors, tics, spasticity (muscle tightness), restless leg syndrome, and other movement disorders. In addition to neurologic movement disorders, BTX has been also used to treat muscle contraction (tension) and migraine headaches, excessive drooling (sialorrhea), excessive sweating (hyperhidrosis), and other conditions for which BTX has been found to be effective. Thus, BTX is not just a cosmetic drug used to treat wrinkles, but it is an effective treatment for a variety of neurologic and non-neurologic conditions.

BTX is a protein that acts by binding to certain nerve endings thus preventing the release of the neurotransmitter acetylcholine. An injection of BTX into the muscle blocks transmission of impulses from the nerve to the muscle causing local and temporary weakness of the target muscle. This process, called "chemodenervation," provides effective relief of dystonias and other disorders manifested by abnormal and unwanted muscular contractions or abnormal secretions. The onset of improvement is often noted within a few days after injection and the benefits usually wear off after 3 to 6 months at which time a repeat injection is needed. Because BTX acts only locally without spreading into the circulation, it does not usually cause any systemic reactions although rare cases of generalized weakness and respiratory compromise have been reported, particularly in children treated with relatively high doses of BTX for spastic cerebral palsy. Most patients obtain safe and substantial relief when used for therapeutic purposes, but a few experience side effects after the treatment. Except for occasional temporary feeling of generalized “flu-like” malaise and weakness, nearly all other side effects are confined to the injected body part. Injections into the eyelids, for example, may result in transient local swelling, droopy eyelids (ptosis), blurring of vision, and tearing. Injections into the neck muscles may cause temporary neck weakness or pain and difficulties with swallowing. Swallowing problems, as well as chewing, speech and voice difficulties, may also result from injections into the jaw and vocal cord muscles. Injections into the arm or hand muscles may cause temporary weakness of fingers and hands. These side effects are usually mild, occur infrequently, and most resolve in a few weeks without any specific treatment. If swallowing problems occur, it is advisable to change to a soft or liquid diet. Any troublesome side effects should be reported to the treating or primary care physician.

Though there are several formulations of BTX approved by the US FDA. Type A BTX formulations include onabotulinumtoxinA (Botox), incobotulinumtoxinA (Xeomin), abobotulinumtoxinA (Dysport), and daxibotulinumtoxinA (Daxxify); type B BTX is called rimabotulinumtoxinB (Myobloc). The injecting clinician selects the formulation based on personal preference and other factors. Although the different types of BTX have similar efficacy and side effect profile, Myobloc is more painful when injected and is more likely to cause immunoresistance with development of blocking antibodies.

BTX treatments do not represent a cure, but they usually provide satisfactory relief of symptoms that can be maintained by repeating treatments when the effects of previous BTX injections begin to wear off. Rarely, some patients become unresponsive to the treatment because they develop blocking antibodies. Such immunoresistance is quite uncommon and occurs only after repeated treatments, usually with relatively high doses or when injected more frequently than every 3 months. There are several ways that the presence of immunoresistance can be detected. The simplest and least expensive way is to inject small amounts of BTX into the inner portion of right eyebrow. As a result of this unilateral brow injection (UBI) the eyebrow is weakened by the injection and one week later the patient is unable to contract the muscle on that side while frowning. This asymmetric frowning indicates that the patient responds to BTX and does not have blocking antibodies – no immunoresistance. If immunoresistance develops to BTX type A, then the formulation must be changed to BTX type B (Myobloc). Although most patients regain their response, unfortunately many develop blocking antibodies (immunoresistance) to this type B BTX.

The BTX injection requires specialized skills and, therefore, only some centers are performing this treatment. The actual cost of the medication and procedure depends on the total dose and sites required to treat the specific condition and will be determined at the time of the visit.

References
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