Spasmodic dysphonia belongs to a family of neurological disorders called dystonias. A dystonia is a movement disorder that causes muscles to contract and spasm involuntarily. Spasmodic dysphonia causes voice breaks and can give the voice a tight, strained quality. People with spasmodic dysphonia may have occasional breaks in their voice that occur once every few sentences. The exact cause of spasmodic dysphonia is unknown. According to the National Institute on Deafness and Other Communication Disorders, research has revealed increasing evidence that most cases of spasmodic dysphonia are in fact neurogenic or having to do with the nervous system.