Overview | Understanding the Disorder | Symptoms | Diagnosis | Treatment

Image "A"Key Glossary Terms

Spasmodic Dysphonia (SD)
A voice disorder resulting from involuntary movements (spasms) of the voice box muscles.

A nervous system problem that causes involuntary movement; dystonia is not a psychological problem; SD is a type of dystonia

Adductor SD (Ad-SD)
Spasms in muscles that close vocal folds, which interrupt speech and cause strained or strangled voice breaks

Abductor SD (Ab-SD)
Spasms in muscles that open vocal folds, which interrupt speech and cause breathy or soundless voice breaks


How is SD treated?
No Cure for SD, but Treatment Options Improve Symptoms

  • Although there is no cure for SD, in most cases treatment can improve symptoms.
  • However, treatment that improves voice symptoms does not affect the course of the disorder. In other words, if a person elects not to be treated, the SD will not become worse.

Patient Self-Help Strategies
Some people with SD find ways to improve their voice on their own. These can include chewing something while talking, speaking while laughing, and speaking in falsetto or in a “cartoon-character” voice.

A trick to the brain: It is thought that maneuvers like these take advantage of the task-specific nature of SD to “fool” the brain into thinking that the person is using the larynx for something other than connected speech. However, over time these strategies generally become less effective.

Botulinum Toxin Injection – Main Therapy for SD
Laryngeal injections of botulinum toxin are the main therapy for SD. Botulinum toxin is a naturally occurring substance that weakens muscle by blocking the release of acetylcholine from nerve endings. Acetylcholine is a substance that triggers muscle contraction.

Effects Are Temporary
The effects of botulinum toxin are temporary, lasting about three months, and dose-dependent, so that the muscle weakness is proportional to the amount of toxin used. Research has found that there is a “plateau effect” at higher doses of botulinum toxin; however, at the typical low doses used for the treatment of SD, there is a consistent dose-dependent response.

 Different Types of Botulinum Toxin
Of the eight types of botulinum toxin that exist, two are available for use in humans – botulinum toxin, type A and botulinum toxin, type B.

  • Botulinum toxin, type A: Has been used to improve voice symptoms of patients with SD in the United States since 1984. In this period, it has been shown to be safe, it improves voice symptoms of SD, and it is recognized as such by the American Academy of Otolaryngology–Head & Neck Surgery.
  • Botulinum toxin, type B: Is now available for unrestricted use. It may be used in those people for whom type A no longer has any effect.

How Botulinum Toxin Treatment Works for SD
The principle behind botulinum toxin treatment of SD is to weaken the muscles that are hyperactive or involved in the involuntary movements or spasms. The muscles that undergo spasms are therefore the ones injected – weakening them will minimize the effects of the spasms on voice.

Type of SD Muscles Injected with Botulinum Toxin, Type A
Adductor SD
Adductor muscles, which close the vocal folds
Abductor SD
Abductor muscles, which open the vocal folds
Mixed SD
Ad + Ab
Injection into both sets of muscles

How Botulinum Toxin Treatment Is Performed

  • Injections Through the Skin
  • Botulinum toxin is usually injected through the skin of the neck into the appropriate spots with the aid of electromyography (EMG).
  • The procedure is performed in a physician’s office. Afterwards, the patient may usually go on with the normal activities of the day.
  • The discomfort associated with the injection commonly disappears after a day or two.
  • More rarely, botulinum toxin may be injected through the mouth under a general or local anesthetic.

(For more information, see LEMG.)

Low Dose in the Beginning

  • The physician can arrive at the correct amount only through experience with each individual case and feedback from the patient. For this reason, a record of the dose and its effect is usually kept.
  • Because there is no means of correcting botulinum toxin muscle weakening before it runs its course, most physicians prefer to begin with a low dose and add toxin as necessary.

Staggered Injections for Ab-SD to Avoid Breathing Difficulty

  • In Ab-SD, the toxin is directed at weakening the muscles that open the vocal folds. Inadequate parting of the vocal folds could result in breathing difficulty, so injections are often staggered, with one vocal fold injected one or two weeks after the first.
  • Sometimes, a treating physician may prefer to treat just one side per three-month “cycle” to minimize these effects.

Adjusting Dose and Frequency of Injections

  • Often, the dose of botulinum toxin can be adjusted to minimize unwanted effects in both types of SD.
  • In the case of Ad-SD, for instance, decreasing the dose can usually shorten the duration of the breathiness, but the overall length of benefit may be decreased. Obviously, each person prefers to be injected as infrequently as possible, but each has a different tolerance for the breathy voice period following the injection. People for whom voice is crucial, like lawyers or schoolteachers, may opt for smaller doses at more frequent intervals.

Determining Side to Inject – One-Sided or Both Sides?

  • Currently there are no standard rules for injecting botulinum toxin to one or both sides.

Two-Sided Injections for Ad-SD

  • Most commonly, injections to both sides are done for Ad-SD. This is based on the notion that the disorder is bilateral and symmetric. However, in certain patients a unilateral injection may be preferable to minimize side effects.

Usually One-Sided for Ab-SD

  • Injections for Ab-SD are typically either on one side only or on one side with a large dose and the other side a small dose. The patient will then return approximately three weeks later for a repeat injection, depending upon the response to the first injection.

Measuring Treatment Success

  • Because the aim of SD treatment is to relieve symptoms rather than cure the condition, the patient’s self-rating of speech and voice is probably the best measure of its effectiveness.

 Common Observations on Treatment Response

Measuring How Much Voice Improved
On a scale of 1-10, with normal voice being 10
How Long Improvement Lasts
Ad-SD Injections can improve voice from a score of 5 (Ad-SD without treatment) to 9 after treatment Benefit lasts about 15 weeks
(usually harder to treat)
Lower improvement rating:
Usually voice improves from a score of 5 (Ab-SD without treatment) to 7 after treatment
Benefit lasts about 10 weeks

What does it feel like to have a botulinum toxin injection?

Done Through the Neck

  • Most botulinum toxin injections are done through the skin of the neck using EMG guidance. The otolaryngologist may or may not inject the skin overlying the voice box with a small amount of numbing medicine. (For more information, see LEMG.)

Injection for Ad-SD

  • For the injection procedure, patients are placed in a completely reclining or semi-reclining position, and a very thin needle is then passed through the skin overlying the voice box into the voice box muscle responsible for moving the vocal folds to the midline (adductor muscles).
  • Once the needle has been verified by LEMG to be in the targeted muscle, the botulinum toxin is injected. The patient will experience a small amount of discomfort from the needle going through the skin and must try not to swallow during the procedure.
  • The patient will often hear the EMG activity, which sounds like television static, and should not be startled by this sound.

Injection for Ab-SD

  • The muscle to be injected is localized by LEMG.
  • The needle is then passed through the skin of the neck, in a similar fashion as for Ad-SD except that the voice box is slightly rotated to allow the EMG needle to find the appropriate muscle (posterior cricoarytenoid muscle) on the posterior part of the larynx.

(For more information, see LEMG and Anatomy & Physiology of Voice Production.)

What to Expect After Injections

Typical Pattern Observed in SD patients

Basis of pattern not understood but probably related to process of nerve recovery after weakness from botulinum toxin, type A injections

First 1-3 days 4 days to 2 weeks 2 weeks to three months – main effect of treatment
  • Usually no effects observed
  • Period of marked improvement or effect
  • Leveling off of improvement
  • Improvement level lasts about 3 months


Key Information

A Note on Aftereffects of Injection

  • In Ad-SD, because the muscles that bring the vocal folds together are initially “over-weakened,” injection is normally followed by a period of breathy, whispery voice and sometimes coughing when drinking liquids. This may last for up to two weeks. Most otolaryngologists aim to adjust the botuli

What dose of botulinum toxin should I receive?

  • There is no standard botulinum toxin dose. The dose and injection sites for each patient with SD must be customized according to the severity of the condition, the patient’s voice demands and response to botulinum toxin.

What are the common complications of SD treatment?

  • There may be some complications with botulinum toxin, type A injections, or none at all. The risk of complications is best discussed with your otolaryngologist.

Complications observed after botulinum toxin, type A injections for SD are described below.

Difficulty Swallowing

  • Difficulty swallowing is probably the most common side effect of botulinum toxin injections. Since the larynx (voice box) lies next to the entrance of the esophagus, and since laryngeal muscles are small and located fairly deep within the neck, toxin may inadvertently reach the esophageal or pharyngeal muscles. Weakening of these muscles, when added to the weakening of the vocal folds that results from treatment, can result in altered or impaired swallowing.
  • More an inconvenience than a danger: Some temporary change in swallowing is reported by up to 17 percent of patients. In the vast majority of cases, this is more of an inconvenience than a danger. However, it is possible to impair swallowing more severely, and even theoretically cause a lung infection from food entering the trachea (windpipe). Because the effect of botulinum toxin is temporary, it is usually necessary only to exercise caution while eating or drinking until the situation returns to normal. This is usually a matter of days or weeks, although in very rare cases the problem may persist for the entire three months that the toxin has effect.
  • Usually observed after the first injection, thereafter not so often: Difficulty with swallowing (especially liquids) following botulinum toxin injection is often most noticeable with the first injection and may decrease with subsequent injections.


  • Although always a possibility when a needle is passed through the skin, there have been no reported cases of infection as a result of botulinum toxin injection performed in a physician’s office with normal attention to cleanliness and sterile technique.

Minor Bleeding

  • Minor bleeding and bruising at the injection site may occur, especially in those patients who take aspirin or blood thinners. Serious bleeding has not been reported.

Side Effects

  • Overall experience with botulinum toxin injections reveals that the treatment remains effective over time and seems to have no important side effects for the patient. It is best for patients to consult their physicians about possible side effects.
  • Muscles treated with botulinum toxin have been shown to decrease in size, but in the larynx this is not noticeable. This decrease in size appears to reverse once treatment is discontinued.

Image Red FlagRed Flag

The safety of botulinum toxin in pregnancy and during breast feeding has not been established. Thus injection should not be administered in these situations.

Muscle-Specific Side Effects

  • Side effects are specific to whether the injected muscle is an adductor or abductor muscle.

In Ad-SD, adductor-specific side effects include:

  • Soft, breathy voice
  • Difficulty drinking liquids
  • Both of these side effects occur because the treated vocal folds are unable to come together completely.

In Ab-SD, abductor-specific side effects include:

  •  Some breathing restriction (since the treated vocal fold is not able to move aside fully)

How to Minimize Side Effects

  • Side effects can be minimized and sometimes even eliminated by altering dose or injection pattern. Feedback information from the patient’s experience with the previous injection is essential in making the necessary adjustments. Therefore, each new injection should be preceded by a discussion between the patient and the physician about the effects of the previous injection.

How long will botulinum toxin type A injections be effective?

Developing Tolerance – Loss of Drug Effect

  • Loss of drug effect, or resistance, to botulinum toxin can occur after many treatments.
  •  Higher doses and more frequent treatments increase the likelihood that a person will become resistant.
  • Resistance is rare among people with SD since the dose used is very small.

con_infoKey Information

Resistance to botulinum toxin is not well understood, but it has been found to occur when the body forms antibodies (the body’s defense mechanism) to the botulinum toxin or associated substances, thereby neutralizing their effectiveness. The body forms antibodies to any foreign substance introduced to it, including the botulinum toxin (which originates from one type of bacteria). Resistance to botulinum toxin can be tested by injecting botulinum toxin into the muscle in the forehead and observing the muscle’s response.

Surgical Treatment – A Second-Choice Treatment

  • Surgery for SD, like surgery for all dystonias, is a second-choice treatment – recommended for patients in whom botulinum toxin treatment is for one reason or another impossible, ineffective, or poorly tolerated. Unfortunately a disappointingly large number of patients have had a recurrence of symptoms months to years following surgery.

Aim of Surgery to Weaken Muscles That Go Into Spasms

  • The goal of surgery for SD is the same as for botulinum toxin treatment: to weaken the muscles that spasm.

Types of Surgical Interventions for SD

Cutting Recurrent Laryngeal Nerve (RLN)

  • Surgeons initially cut or crush the nerve to the vocal fold, called the recurrent laryngeal nerve.
  • Despite encouraging initial results, about two-thirds of patients develop symptoms of SD again within three years.
  • Furthermore, although the SD symptoms return, the paralysis that results from the cutting of the RLN remains – a condition that has its own drawbacks.

(For more information, see Vocal Fold Paresis/Paralysis.)

Cutting Superior Laryngeal Nerve (SLN) and Manipulating the Larynx to Reduce Effect of Spasms on Voice

  • Surgeons have also tried cutting the secondary nerve to the larynx, known as the superior laryngeal nerve, and manipulating the larynx so the vocal folds lie farther apart (lateralization thyroplasty) or are under less tension (anterior commissure release). None of these techniques have resulted in satisfactory long-term control of symptoms.

Cutting Both Nerve and Muscle: Thyroarytenoid (TA) Neuromyomectomy

  • One surgical procedure being done in Japan involves removing some of the thyroarytenoid muscle (the muscle within the vocal fold) and nerve innervating it. This surgery is called a TA neuromyomectomy.
  • The results of this procedure have been very favorable. However, the long-term success of this surgical procedure in other countries has yet to be demonstrated.

(For more information, see Anatomy & Physiology of Voice Production.)

Selective Denervation-Reinnervation – Cutting the Nerve That Causes Spasms and Replacing It With Normal Nerve

  • Currently, a procedure known as selective laryngeal adductor denervation-reinnervation is being carefully studied. In this operation, nerves to two of the muscles that close the vocal folds (adductors) are cut (denervation) and replaced (reinnervated) with nerves from muscles that are normal (not involved in the dystonia, i.e., no spasms). Initial results, as in other surgical approaches, have been promising.
  • Long-term results are not yet well known.

con_infoKey Information

Non-Treatment Not Harmful

  • Available treatments for all forms of SD are able only to improve or minimize symptoms. Opting not to be treated has no effect on the underlying central nervous system disorder. Patients should only continue with treatment if they feel it is beneficial.

Other Treatments

Voice Therapy

  • Voice therapy by itself has not been useful in controlling the symptoms of SD. However, voice therapy can help control the side effects of treatment and help the patient manage the anxiety that often worsens the symptoms of SD.

Voice therapy may be helpful following botulinum toxin treatment by helping the person:

  • Eliminate the body’s poor compensation behaviors
  • Adjust to the changes in the voice from treatment
  • Maximize the beneficial effects of the botulinum toxin treatment

Psychological/Psychiatric Treatment

  • SD is an organic disorder of the central nervous system. As a result, psychological/psychiatric treatment is not an effective primary treatment.
  • However, any chronic condition can be emotionally and psychologically draining. SD is especially so because it affects the voice. A mental health professional may help SD patients better handle the stresses associated with SD.

Oral Medication Treatment

  • Many medications that act on the central nervous system may be beneficial in dystonia. Unfortunately, at doses that relieve symptoms, significant side effects–like sedation and memory loss – are common.
  • In most cases of SD, oral medication is not used at all or is used only as an auxiliary therapy. A neurologist specializing in movement disorders is usually the most appropriate person to consult regarding medication. For this reason, many otolaryngologists who specialize in SD recommend evaluation by such a specialist at some point.

con_infoA Final Word

SD Can Be Frustrating

  • SD is a frustrating, chronic condition for which no cure is currently known. However, it is only rarely associated with other diseases. In most cases, treatment can substantially improve symptoms, often resulting in a near-normal voice.

Open Patient-Physician Communication Important

  • Because, in the end the affected person is the best judge of his or her voice function, honest and open communication between the doctor and patient is essential in getting the most out of treatment and overcoming the disorder.

Further Information Is Available

Patient Associations and Support Groups

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Patient education material presented here does not substitute for medical consultation or examination, nor is this material intended to provide advice on the medical treatment appropriate to any specific circumstances.

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