Spasmodic dysphonia is a neurological disorder affecting the voice muscles in the larynx, or voice box. When we speak, air from the lungs is pushed between two elastic structures—called vocal folds or vocal cords—with sufficient pressure to cause them to vibrate, producing voice. In spasmodic dysphonia, the muscles inside the vocal folds experience sudden involuntary movements—called spasms—which interfere with the ability of the folds to vibrate and produce voice.

Spasmodic dysphonia can affect anyone. It is a rare disorder, occurring in roughly one to four people per 100,000 people. The first signs of spasmodic dysphonia are found most often in people between 30 and 50 years of age. It affects women more than men. In some cases, spasmodic dysphonia may run in families.

The cause of spasmodic dysphonia is unknown. In rare cases, psychogenic forms (originating in a person’s mind) of spasmodic dysphonia do exist. However, in most instances, the muscle spasms are caused by abnormal functioning in an area of the brain called the basal ganglia.

Symptoms of spasmodic dysphonia generally develop gradually and with no obvious explanation. Although the risk factors for spasmodic dysphonia have not been identified, the voice symptoms can begin following an upper respiratory infection, injury to the larynx, voice overuse, or stress.

Spasmodic dysphonia causes voice breaks and can give the voice a tight, strained quality. People with spasmodic dysphonia may have occasional breaks in their voice that occur once every few sentences. Usually, however, the disorder is more severe and spasms may occur on every other word, making a person’s speech very difficult for others to understand. At first, symptoms may be mild and occur only occasionally, but they may worsen and become more frequent over time. Spasmodic dysphonia is a chronic condition that continues throughout a person’s life.

The types of spasmodic dysphonia are:

• Adductor spasmodic dysphonia is the most common form of spasmodic dysphonia. It is characterized by spasms that cause the vocal folds to slam together and stiffen. These spasms make it difficult for the vocal folds to vibrate and produce sounds. Words are often cut off or are difficult to start because of muscle spasms. Therefore, speech may be choppy. The voice of someone with adductor spasmodic dysphonia is commonly described as strained or strangled and full of effort. The spasms are usually absent—and the voice sounds normal—while laughing, crying, or shouting. Stress often makes the muscle spasms more severe.
• Abductor spasmodic dysphonia is characterized by spasms that cause the vocal folds to open. The vocal folds cannot vibrate when they are open too far. The open position also allows air to escape from the lungs during speech. As a result, the voice often sounds weak and breathy. As with adductor spasmodic dysphonia, the spasms are often absent during activities such as laughing, crying, or shouting.
• Mixed spasmodic dysphonia, a combination of the above two types, is very rare. Because both the muscles that open and the muscles that close the vocal folds are not working properly, it has features of both adductor and abductor spasmodic dysphonia.

Spasmodic dysphonia may co-occur with other dystonias that cause involuntary and repetitious movement of such muscles as the eyes; face, body, arms, and legs; jaws, lips, and tongue; or neck.

There is currently no cure for spasmodic dysphonia; therefore, treatment can only help reduce its symptoms. The most common treatment for spasmodic dysphonia is the injection of very small amounts of botulinum toxin directly into the affected muscles of the larynx. The toxin weakens muscles by blocking the nerve impulse to the muscle. Botulinum toxin injections generally improve the voice for a period of three to four months, after which the voice symptoms gradually return. Reinjections are necessary to maintain a good speaking voice.

Behavioral therapy (voice therapy) is another form of treatment that may work to reduce symptoms in mild cases. Other people may benefit from psychological counseling to help them accept and live with their voice problem.

In some cases, augmentative and alternative devices can help people with spasmodic dysphonia to communicate more easily. For example, some devices can help amplify a person’s voice in person or over the phone. Special software can be added to a computer or handheld device such as a personal digital assistant (PDA) or cell phone to translate text into synthetic speech.

When more conventional measures have failed, surgery on the larynx may be performed. Long-term benefits and effects of this procedure are unknown.