Botulinum neurotoxin injections to treat symptoms of spasmodic dysphonia

Botulinum neurotoxin (BNT) is a common treatment used to reduce the symptoms of spasmodic dysphonia since the mid-1980s. Botulinum toxin is derived from the bacterium Clostridium botulinum. It is a nerve “blocker” that binds to the nerves that lead to the muscle and prevents the release of acetylcholine, a neurotransmitter that activates muscle contractions. After a short period of time, typically several months, the nerve endings regenerate, the muscle gradually regains strength and muscle contractions or “spasms” return. It is recognized as an effective treatment by the American Academy of Otolaryngology – Head and Neck Surgery.

In spasmodic dysphonia, laryngeal muscles spasm because too many of the wrong type of signals travel from the brain through the nerves and into the muscles. Botulinum neurotoxin, a biologic product, is injected directly injected into the affected muscles. Botulinum neurotoxin blocks these nerve signals, reducing the number and severity of the spasms.

BNT generally lasts an average of three months but duration of benefit depends on several factors such as severity of the SD, dosage received, unilateral or bilateral injection and the presence or absence of tremor.

It may require several injections to establish the optimal individualized dose, as it can be different for each person. Optimal dosage is a balance of duration of injection side effects/breathiness and duration of clear voice. Some may prefer to have a stronger dosage with a longer period of breathiness after the injection and a longer duration of optimal voice (requiring fewer shots per year), while others may prefer to minimize the side effect duration to opt for shorter lasting, more frequent injections. Two different individuals may also have different results from the same dosage (due to differing anatomy, neurology, severity of SD etc.) so initial dosages must be trialed and tailored to fit the individual’s needs. Individuals may choose to time injections around important speaking events (i.e. presentations, weddings). Unilateral injections may offer a good option for some individuals desiring less side effects.

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