CAUSES:

The cause of spasmodic dysphonia is unknown. The general medical consensus is that SD is a central nervous system disorder and a focal form of dystonia. Dystonia is the general neurological term for a variety of problems characterized by excessive contraction of muscles with associated abnormal movements and postures.

Spasmodic dysphonia is similar to other focal dystonias such as blepharospasm (involving the eyelids), oromandibular dystonia, (involving the jaw and tongue), cervical dystonia or spasmodic torticollis (involving the neck), and writer's cramp (involving the hand).

Dystonia disorders are thought to be due to abnormal functioning in the area of the brain called the basal ganglia. The basal ganglia, which are structures situated deep in the brain that help coordinate movements of the muscles throughout the body.

Onset is usually gradual with no obvious explanation. Symptoms usually occur in absence of any structural abnormality of the larynx, such as nodules, polyps, carcinogens, or inflammation. Researchers are investigating possible mechanisms involved in the triggering of SD including familial factors and/or injury that may lead to central nervous system changes in laryngeal motor control.

SD may co-occur with other dystonias such as blepharospasm, oromandibular dystonia, or cervical dystonia.