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Spasmodic Dysphonia

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

Electromyography (EMG) of the larynx is a powerful diagnostic tool with important applications in the study and treatment of voice disorders. Laryngeal EMG allows us to examine electrical activity in the muscles that move the vocal folds. By studying this electrical activity, important information can be gained about the activity of the vocal folds during speech.

Laryngeal EMG is especially useful in studying movement disorders of the larynx. For example, in cases of vocal fold immobility, results of an EMG can help determine the diagnosis and predict whether recovery will occur. If the EMG indicates that there is little chance of recovery, a vocal fold medialization procedure can be done to help restore the voice.

Laryngeal EMG is somewhat similar to electrocardiography (called EKG) of the heart. However, in EKG the measuring electrodes can be simply placed in the chest since the heart is a large strong muscle. The laryngeal muscles are much smaller, so different techniques must be used.

In order to do laryngeal EMG, small electrodes must be placed into the muscles of the larynx. These electrodes can either be thin needles or fine wires. The needle electrodes used in EMG are insulated along their entire length except for a small bare spot at the end. Fine wire EMG is done using insulated wire that is thinner than a human hair.

Good signals can be obtained from either type of electrode. The fine wires are somewhat more difficult to insert, but they are so light that the person being tested can easily talk with them in place. Needles, in contrast, are easier to place but they are quite bulky and can interfere with speaking. They are therefore used when only a few speech tasks need to be tested.

The type of electrode used and the muscles studied depends on the disorder under investigation For example, in unilateral vocal fold immobility often only a needle electrode study is necessary. In this case, there are usually two important questions to answer: is there evidence of nerve injury, and if so what is the likelihood of recovery.

There are certain types of electrical activity that indicate a permanently damaged nerve and others which indicate that there might be recovery. For example, when a nerve recovers it often send connections (called synapses) to a greater number of muscle fibers than before the injury. When the nerve fires, the electrical signal can therefore be somewhat bigger and broader than before. This type of pattern is called a polyphasic signal, is a good sign that there is some recovery going on.

Another type of nerve activity, called a fibrillation potential, indicates that the nerve is not recovering well. If this activity is seen in a paralyzed vocal fold, it indicates that the chances of recovery are not good and some other treatment might be appropriate. In the tracing below, the fibrillation waves are the sharp upward spikes.

fibrillation potentials

Another type of signal is called a positive sharp wave, shown below. The initial portion of the wave has a positive polarity (which is downward on the tracing). This pattern is also typical for denervation of the muscle, meaning that it has lost its nerve supply.

positive sharp waves