Spasmodic dysphonia (or laryngeal dystonia) is a voice disorder characterized by involuntary movements of one or more muscles of the larynx (vocal folds or voice box) during speech.
The three types of spasmodic dysphonia (SD) are adductor spasmodic dysphonia, abductor spasmodic dysphonia and mixed spasmodic dysphonia.


Adductor spasmodic dysphonia
In adductor spasmodic dysphonia, sudden involuntary muscle movements or spasms cause the vocal folds (or vocal cords) to slam together and stiffen. These spasms make it difficult for the vocal folds to vibrate and produce voice. Words are often cut off or difficult to start because of the muscle spasms. Therefore, speech may be choppy and sound similar to stuttering. The voice of an individual with adductor spasmodic dysphonia is commonly described as strained or strangled and full of effort. Surprisingly, the spasms are usually absent while laughing, singing, speaking at a high pitch or speaking while breathing in. Stress, however, often makes the muscle spasms more severe.


Abductor spasmodic dysphonia
In abductor spasmodic dysphonia, sudden involuntary muscle movements or spasms cause the vocal folds to open. The vocal folds can not vibrate when they are open. The open position of the vocal folds also allows air to escape from the lungs during speech. As a result, the voices of these individuals often sound weak, quiet and breathy or whispery. As with adductor spasmodic dysphonia, the spasms are often absent during activities such as laughing or singing.


Mixed spasmodic dysphonia
Mixed spasmodic dysphonia involves muscles that open the vocal folds as well as muscles that close the vocal folds and therefore has features of both adductor and abductor spasmodic dysphonia.