Spasmodic Dysphonia (SD), or Spastic Dysphonia, occurs when the larynx spasms with no other accompanying motor speech disorder or laryngeal issue. It is a focal dystonia of the larynx where the larynx spasms involuntarily during speaking. It occurs only when the patient speaks, as there is no evidence of laryngeal spasms during vegetative vocal behaviors like coughing, crying, or laughing. Stress seems to make symptoms worse. SD usually appears around age 40, and most often in females. A combination approach to treatment is most effective, involving pharmacological treatments and behavioral voice therapy to reduce laryngeal tension, regulate breath flow and decrease effort during speaking.
Adductor Spasmodic Dysphonia is the most common form of SD with a strangled quality to the voice during speech as the vocal folds hyperadduct (come together more than necessary) and spasm. Public figures including Diane Rehm and Robert Kennedy Junior suffer from adductor SD and have brought the condition into the media. You can view this here. Sometimes those who suffer from SD also suffer from vocal tremor, about half in fact. Individuals with adductor SD find their symptoms worsen during speech that is voiced (like the sounds /m/, /b/, /d/, and /g/) versus voiceless (like /s/, /p/, /t/, or /k/). Shouting is difficult for patients with adductor SD and some find that talking in a higher pitch will briefly reduce the frequency of the spasms.
Abductor Spasmodic Dysphonia is the least common form and is the exact opposite of adductor SD. The vocal folds involuntarily separate during phonation and give the person a breathy sound in the middle or sounds, words and sentences. Voiceless sounds are worse here, (/s/, /p/, /t/, /k/.) It takes maximum effort to speak and fatigue is ever present, as patients have a hard time keeping the vocal folds closed during phonation requiring more air use because of the uncontrolled air escape.
Botulinum toxin, or Botox, is used to treat SD by inhibiting acetylcholine release and temporarily paralyzing the vocal fold muscles (thyroarytenoid) or surrounding muscles, depending on the type of SD a patient has. There have been over 100 studies recently with variable methodology showing positive effectiveness of using Botox to treat SD. The injections usually last 3-12 months, and it may take up to 2 -3 weeks for a positive effect to be noticed.
Sources: Clinical Voice Pathology: Theory and Management 4th Edition Stemple, Glaze & Klaben.
Watts,C, Whurr R, Nye C. Botulinum toxin injections for the treatment of spasmodic dysphonia (Review), (2010) The Cochrane Collection.
Laryngeal Evaluation: Indirect Laryngoscopy to High-Speed Digital Imaging. Katherine A. Kendall and Rebecca J. Leonardk, Thieme publishing. 2010.