This page will give a brief description of the voice disorder known as spasmodic dysphonia. A separate page describes treatment of spasmodic dysphonia using Botox injections. A dystonia is a disorder of the central nervous system in which there is increased contraction of the muscles. This disorder can affect a large number of muscles, which is called a generalized dystonia, or it can affect just one or two muscle groups in which it is called a focal dystonia. More information on dystonias is available .
Spasmodic dysphonia is a dystonia in which affects only the muscles of the larynx.
The exact cause of this dystonia is currently unknown, but is believed to involve a region deep in the brain called the basal ganglia. In spasmodic dysphonia, this area of the brain sends incorrect messages to the muscles controlling the movement of the vocal folds, causing them to contract inappropriately. There are several types of spasmodic dysphonia. The most common is called adductor SD and it occurs when the muscles that bring the vocal folds together contract too strongly. In adductor SD the voice has a very strained or strangled sound, with occasional breaks when the air cannot escape.