Spasmodic dysphonia is one of a group of neurologic disorders called dystonias. A dystonia is a movement disorder characterized by forceful, inappropriate contraction of muscle groups. With spasmodic dysphonia, the intrinsic laryngeal muscles are involved.

There are two primary types of spasmodic dysphonia. The most common type is adductor spasmodic dysphonia. This occurs when the muscles that close the vocal folds (thyroarytenoids) contract with excess force. Abductor spasmodic dysphonia involves the muscles that open the vocal folds (posterior cricoarytenoids). A "mixed" form involving both the abductor and adductor muscles also exists.

Symptoms: The symptoms of spasmodic dysphonia depend on which form is present. The adductor type produces a strained or strangled voice quality. Abductor spasmodic dysphonia usually presents with a breathy and effortful voice. Both types cause abrupt breaks in phonation and decreased intelligibility.

Causes: The precise cause of spasmodic dysphonia is unknown and may involve multiple factors. It is thought that spasmodic dysphonia primarily involves a disorder of the midbrain that causes the transmission of inappropriate neural impulses to the involved muscles. Recent research has shown that susceptibility to spasmodic dysphonia may be of genetic origin.

Treatment: Currently, the most effective treatment for spasmodic dysphonia is the use of botulinum toxin (Botox). Botox is injected into the laryngeal muscles via the neck (just under the Adam's apple) or through the mouth using a special needle that curves over the tongue. Botox interferes with the transmission of the electrical impulses that result in the inappropriate contraction of the laryngeal muscles and prevents the spasms associated with spasmodic dysphonia. Botox treats the symptoms of spasmodic dysphonia, but it does not provide a cure for the cause of the disorder.

The effects of Botox injections are usually apparent within 24 hours and last for three to six months. Risks and discomfort during the procedure are minimal. Patients may experience a weak, breathy voice and mild difficulty swallowing for one to two weeks after the procedure. The major disadvantage of the procedure is that it has to be repeated on a regular basis to maintain the benefit.