The common name for laryngeal dystonia. Dystonia is a neurologic movement disorder, caused by a problem in the nervous system. The vocal folds vibrate normally, but they spasm intermittently during speech. There are three different types of spasmodic dysphonia (SD): abductor SD, adductor SD, and mixed abductor and adductor SD. Term found in Types of Voice Disorders: Spasmodic Dysphonia.