Causes of Spasmodic Dysphonia
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, or originating in a person's mind, rather than from a physical cause. In rare cases, psychogenic forms of spasmodic dysphonia do exist; however, in most instances, the muscle spasms are caused by abnormalities in the central nervous system (the brain).

A disorder that involves involuntary muscle contractions is also called a dystonia; therefore, another name for spasmodic dysphonia is laryngeal dystonia. Spasmodic dysphonia is considered a form of focal dystonia, a neurological disorder that affects muscle tone in one part of the body. Writer's cramp is another type of focal dystonia. Other dystonias can affect multiple regions of the body or the entire body.

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.

Spasmodic dysphonia is thought to be caused by abnormal functioning in an area of the brain called the basal ganglia. The basal ganglia consist of several clusters of nerve cells deep inside the brain. They help coordinate movements of the muscles throughout the body. Recent research has found abnormalities in other regions of the brain, including the brainstem, the stalk-like part of the brain that connects to the spinal cord.

Symptoms of spasmodic dysphonia generally develop gradually and with no obvious explanation. Some people with spasmodic dysphonia also have vocal tremor, a shaking of the larynx and vocal folds that causes the voice to shake. 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.