Published online by Cambridge University Press: 02 December 2009
Introduction
Botulinum toxin (BoNT), the most potent biologic toxin, is a highly effective therapeutic tool in a variety of neurologic and other disorders. In minute doses it has the ability to block Ach release and, therefore, has been exploited to relieve disease symptoms associated with muscle hyperactivity. Intramuscular injection of BoNT produces a chemodenervertion at the neuromuscular junction that results in reversible partial paralysis. While used primarily for conditions characterized by abnormal, excessive, or inappropriate muscle contractions, BoNT is also increasingly used in the management of a variety of ophthalmologic, urologic, gastrointestinal, orthopedic, cosmetic and dermatologic disorders.
As the use of BoNT continues to increase, the antigenicity of BoNT and development of immunoresistance secondary to blocking antibodies has continued to be a pressing concern. A certain percentage of patients receiving repeated injections develop blocking antibodies (immunoresistance) against BoNT (BoNT-Abs) causing them to be completely resistant to the effects of subsequent BoNT injections. This is termed secondary resistance. Primary resistance refers to lack of response to initial BoNT treatment, which is extremely rare, and may be due to pre-existing BoNT-Abs, possibly as a result of prior immunization against botulism. The frequency of neutralizing or blocking antibodies (immunoresistance) against BoNT is not known. This lack of information is partly due to a paucity of well-designed epidemiological studies utilizing appropriate assays to determine the frequency of blocking antibodies in a prospectively followed population of BoNT-treated patients.
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