Overview, Side Effects

Overview

Botulinum toxin injection therapy (also known as "BOTOX® therapy") is used to treat dystonia—a neuromuscular disorder that produces involuntary muscle contractions, or spasm—that affects muscles that control movement in the eyes, neck, face, limbs, voice box, or the smooth muscle in the bladder. The goal of the therapy is to reduce muscle spasm and pain.

This potent neurotoxin is produced by Clostridium botulinum, a bacterium that causes food poisoning (botulism). There are seven known types of C. botulinum toxin, but only types A; (BOTOX® Cosmetic) and B (Myobloc®) are used as medical treatments.

Botulinum toxin has proven to be useful in the treatment of many forms of dystonia, including the following:

• blepharospasm–forceful involuntary closure of the eyelids
• strabismus–misalignment of the eyes
• hemifacial spasm–sudden contraction of the muscles on one side of the face
• spasmodic torticollis, or cervical dystonia–muscle spasm in the neck that causes the head to turn to one side, and sometimes forward or backward
• oromandibular dystonia–continuous spasms of the face, jaw, neck, tongue, larynx, and in severe cases, the respiratory system
• urinary retention–severe inability to urinate that requires catheterization
• spasmodic dysphonia–spasm of the vocal cords that causes sudden disruption of speech
• stuttering–repetitions of parts of words and whole words, long pauses, elongated sounds
• voice tremor–quavering vocalization
• limb spasticity (e.g., following stroke)

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Neurons generate new nerve endings that reactivate the dystonia, so improvement is not long lasting, and treatment is usually repeated every 3 to 4 months. Physical or occupational therapy usually is undertaken to stretch and restore normal muscle function. Some patients develop antibodies to the toxin over time, rendering the treatment ineffective.

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Side Effects
Botulinum toxin therapy is a safe and effective treatment when given in very small amounts by a qualified neurologist. Some patients experience temporary weakness in the group of muscles being treated. For example, ptosis (drooping eyelid) can develop after treating blepharospasm. Flu-like symptoms develop in some, but rarely.

In April 2009, the U.S. Food Administration (FDA) announced a black box warning requirement for all botulinum toxin products, including BOTOX®, BOTOX® Cosmetic, Myobloc®, and a newly-approved product called Dysport®. This warning was issued in response to reports that the effects of botulinum toxin can spread from the injection site to other areas of the body and cause difficulty speaking, swallowing, and breathing; muscle weakness; loss of bladder control; drooping eyelids; and blurred vision. The goal of the FDA warning is to better inform physicians and patients about the potential risks associated with botulinum toxin injections.

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