Overview. Spasmodic dysphonia is a voice disorder caused by involuntary movements of one or more muscles of the larynx or voice box. Individuals who have spasmodic dysphonia may have occasional difficulty saying a word or two or they may experience sufficient difficulty to interfere with communication.pasmodic dysphonia causes the voice to break or to have a tight, strained or strangled quality. While the cause of spasmodic dysphonia is unknown, most cases are believed to be neurogenic (having to do with the nervous system) in nature.