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 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. Spasmodic dysphonia can affect anyone. The first signs of this disorder are found most often in individuals between 30 and 50 years of age.
More women appear to be affected by spasmodic dysphonia than are men.
The cause of spasmodic dysphonia is unknown. Because the voice can sound normal or near normal at times, spasmodic dysphonia was once thought to be psychogenic, that is, originating in the affected person s mind rather than from a physical cause. In some cases, spasmodic dysphonia may run in families and is thought to be inherited. Research has identified a possible gene on chromosome 9 that may contribute to the spasmodic dysphonia that is common to certain families. In some individuals the voice symptoms begin following an upper respiratory infection, injury to the larynx, a long period of voice use, or stress.