Botulinum toxin injection 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, 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) 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.

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.

Side Effects

This 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.