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
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.