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Botox Injection for Laryngeal Spasmodic Dysphonia

  1. Anatomy
  2. Examining the larynx
  3. Voice Science
  4. Voice Disorders
  5. Vocal fold immobility
  6. Tracheotomy

Introduction

Spasmodic dysphonia (SD) is a type of neurologic disorder called a dystonia. It affects the muscles of the larynx. This page describes SD and its treatment using a medication called botulinum toxin (Botox).

A general description of dystonias is also available. The basic problem in SD is that the muscles of the larynx contract too strongly during speech. The muscles themselves are normal, but their neurological control is abnormal. The cause of SD is believed to originate in a part of the brain called the basal ganglia.

The are several different types of SD. In the most common variant the muscles that close ("adduct") the folds contract too tightly. This condition, called adductor spasmodic dysphonia, produces a strained or strangled sound to the voice. In a less common variant the problem is with the muscles that open, or "abduct" the vocal folds. Some individuals have mixed SD, or characteristics of both adductor- and abductor-type dystonia. SD can also be associated with tremor.

Botox can minimize the symptoms of SD when injected into muscles of the larynx. This page will provide some information about how Botox works, the general technique of the botulinum toxin injections, as well as some of the possible complications.

The image to the left shows a cross section of the vocal folds, viewed from above. (A description of the anatomy and function of the larynx is given elsewhere). For the more common adductor SD, the botox is usually injected into the thyroarytenoid ("thigh'-row uh-rit'-uh-noyd") muscle. In a few cases, better results may be obtained with an injection into a muscle called the lateral cricoarytenoid (not shown in this diagram).

For the less common variant of abductor spasmodic dysphonia, the muscles that open the vocal folds must be weakened. This muscle is called the posterior cricoarytenoid and it runs from the cricoid to the arytenoid. (The arytenoid is a small piece of cartilage attached to the back of the vocal folds.

General Information

The effect of the botulinum toxin is to weaken the injected muscles. Although the source for the dystonia appears to be at the base of the brain, we are able to treat the disorder by injecting the involved muscle. Therefore it is important to remember that Botox does not treat the cause of dystonia, but only provides temporary symptomatic relief. Although the muscle is still receiving abnormal signals from the brain, it cannot contract as strongly as before. This weakness provides the relief patients experience with Botox treatments.

During the Botox injection, you will lie down in an examination chair with your head extended back over a pillow. It is helpful if you wear a shirt or blouse that has an open neck. A local anesthetic is injected first so that the skin and sensitive areas near the vocal folds are not stimulated when the needle is placed.

The Botox is injected through a very small needle which is connected by a wire to an electromyography (EMG) machine that records the activity of the muscle. The placement of the needle into the muscle is verified by the electrical signals shown on the EMG machine. Once the EMG signal indicates that the needle is in the correct muscle, the medication is injected. There generally is minimal discomfort associated with the injection. The entire procedure takes about fifteen minutes.

This image shows a side view of the manner in which the botox is injected. After numbing the area with a local anesthetic, the needle is passed under the thyroid cartilage into the muscles of the vocal fold. The entire procedure takes just a couple of minutes.
The image to the left shows example of EMG recordings of the larynx. The recordings shown here are from three muscles; the left and right thyroarytenoid muscle, and one of the two posterior cricoarytenoid muscles. For the more common adductor spasmodic dysphonia, the injection is done into the thyroarytenoid muscle.

One should not eat or drink anything for 45 -60 minutes after the injection. The anesthetic numbs the throat and may cause coughing after swallowing. Some patients may cough up some blood-tinged sputum during the first 24 hours after the injection. A small amount of bleeding may occur when the needle is inserted, and this can appear in the sputum. The neck may be slightly sore for a day or two from having the needles inserted, but this usually passes without any intervention needed. After a Botox injection it is best to not take aspirin or ibuprofen (Advil, Motrin) since these interfere with blood clotting and can lead to bleeding.

The effects of Botox begin about 12-24 hours after the injection. Its effect is almost always noted by 48 - 72 hours and the full effect is established usually by one week, but sometimes as late as two weeks.

Botox prevents the release of one of the body's neuro- transmitters at the connection between the nerve and the muscle, causing weakness of the muscle. Over time, the connection between the nerve and the muscle grows back, and therefore, the effect of Botox is temporary. In most cases, the effect of Botox lasts 2-4 months.

It is important to remember that, although Botox is derived from the botulinum organism, the organism itself is never injected. The material that is injected is the muscle relaxant produced by the botulinum bacteria. For SD, an extremely tiny amount is injected since the muscles of the larynx are so small.

Since the severity of the disorder in each individual is different, the dosage for the first one to three injections is calculated by estimating the degree of dystonia. Sometimes too little is given and relief is minimal. Sometimes, if an individual patient is very reactive to the botulinum toxin, an exaggerated response leading to significant weakness can be seen. After one or two sessions, the right dose for each individual can usually be found. There appears to be some variation even with identical injections so that in some eases, a greater effect or a lesser effect is experienced when compared to a previous injection with the same amount of Botox.

Botox injections almost always cause an exaggerated effect during the first week or two after the injection. This can result in a very breathy or high-pitched voice. This effect wears off after about two weeks and the more therapeutic effects of Botox become evident.

Possible Complications from Botox Injection

The vocal folds close tightly when we swallow to help prevent food from entering the lungs. This protective measure is weakened after Botox injections. In most cases this effect causes minimal or no problems. However, it there is an exaggerated effect, there can be symptomatic aspiration. In rare cases, a feeding tube must be placed to provide nutrition. After injection of one posterior cricoarytenoid muscle, a laryngeal examination is usually performed prior to injection of the other side to be sure that the muscle that move the vocal folds apart are working well. If both muscles are weakened, this can cause breathing problems.

Some individuals who receive very large injections of Botox for conditions such as torticollis ("wry neck") have developed antibodies to the Botox. This limits the effectiveness of the medicine, requiring larger doses. However, the dose of Botox used in laryngeal dystonia is much much smaller than torticollis, and antibody formation is seldom seen in spasmodic dysphonia.

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