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 (see figure). 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 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.