The injection
There are two common methods for injecting the muscles causing AB SD (ABductor Spasmodic Dysphonia). The original and most widely used method is for the physician to grasp the voicebox (the thyroid cartilage) and rotate it toward one side. A long needle is then passed in from the side of the neck until it reaches the back side of the voice box. When the muscle is identified by an EMG (ElectroMyoGraphic) signal, the Botox medication is instilled. The procedure is repeated from the opposite side.
The method that I use and was taught to me by Bob Bastian (Meleca, et al) is translaryngeal - meaning through the voice box. It is similar to the ADductor approach. Numbing medication is placed in the skin over the front of the voice box and then squirted into the voice box. This causes a brief cough (and a bitter taste from the medication) and then numbs the lining of the voice box which is otherwise very sensitive. You know how sensitive it is if you have ever had liquid go down the wrong pipe and began coughing.
After it is numb, a needle is passed through the front of the voice box and out the back. As the needle passes through the cartilage at the back of the voice box, it should be in the PCA muscle. I use the EMG to identify when I am in the muscle and may ask you to sniff. This activates the muscle and causes more activity on the EMG. If the needle goes to far, it may still be in a muscle, but that muscle would be the swallowing tube (the esophagus). It would not activate with a sniff.
Most typically, both sides (both PCA muscles) would be injected. There are two exceptions. I have seen patients where only one side was spasming. The most common reason however, is fear on the part of the physican or patient. I have generally found that fear to be unfounded, but allow me to proceed. When the muscles opening the voice box widely are weakened, they can't open widely. This leads to noisy breathing, most particularly when breathing in. Breathing out is fine, but normally the vocal folds move away from each other on breathing in and when they don't, they will vibrate. This creates a sound during breathing in which is a bit scary if one is unprepared. Usually, the dose of Botox is low enough that the PCA muscles still work a bit. However, with exercise, there will tend to be shortness of breath. This is the opposite of Botox injections for ADductor SD which cause a breathiness when there is a bit too much medication.
If you have this breathing problem, here is a hint. The slower you breath, the less the vocal cords will pull together and the less noise you will make breathing. This is that high school physics you learned called The Bernoulli Principle, in action. Fast airflow though a narrow area lowers the air pressure and in this case sucks the weakened vocal cords closer together.
The initial wait
For a day or two after the injection your voice will usually be unchanged. Approximately 24-72 hours from the injection the spasms begin to diminish and the voice may be stronger and steadier. At the same time you may (but not necessarily) start to experience this shortness of breath. In other words, the breathing symptoms may not happen at all; they may be subtle; or they could be very noticeable and even uncomfortable and anxiety-provoking.
The better voice but I'm short of breath phase
This phase may last from a few days up to many weeks. Again, some don´t experience any shortness of breath. During this phase, you will notice that your voice is better, even though some spasms remain. You may also experience some involuntary vocal sounds when you breathe in suddenly.
The talking is golden phase
For 1-3 months after the initial side effect phase has passed, the voice often seems virtually normal. Talking is a pleasure, and some almost forget they even have spasmodic dysphonia during this time.
The spasms are increasing phase
Typically, during the second to fourth month after your injection you may find that your voice is again worsening. When you notice this happening, you may not need to return immediately for another injection, because you may still have several to many weeks of reasonable vocal function. As spasms become more noticeable, you should consult your calendar and arrange another injection appointment.
The unsatisfying response
Achieving a good result for abductory SD can be more difficult than for adductory SD. It usually requires more than one injection to get the correct dose. Generally everyone involved is hesitant to give too big of a dose because of the discomfort of the side effects and because there is no good treatment for the side effects, only waiting for them to resolve on their own.
The PCA muscle
The main muscle that causes AB SD is the PCA (Posterior Cricoarytenoid Muscle), purple in this photo. It is located on the back of the voice box. It is the muscle that opens the vocal folds widely for breathing. It is at its most active during sniffing. It should be basically at rest during speaking. If it contracts during the making of a sound (phonation), then the vocal cords open and a breath of air comes out. That is an ABductor spasm. To hear a sample of a female voice with ABductor spasms, play the following.
To learn more about the anatomy in this picture.