Spasmodic dysphonia (SD) is a type of dystonia, a neurologic disease that causes involuntary movements. There are two main types of SD. Adductor SD (AdSD) causes the vocal folds to come together (adduct) inappropriately during voicing, and makes up about 85-90% of SD cases. Abductor SD (AbSD), on the other hand, makes the vocal folds come apart (abduct) during connected speech.
SD usually affects adults, with a typical onset of symptoms in the thirties or fourties. The cause is unknown, and there do not appear to be any behaviors or environmental factors that increase the chance of contracting SD. The disease does not show a hereditary link in the vast majority of cases.
In AdSD, the vocal folds come together too tightly during speech, causing strained, strangled breaks in the voice. In AbSD, the vocal folds part, causing breathy or soundless breaks. In both cases, the voice breaks are irregular, and the severity of the symptoms can vary from day to day, or even over the course of a single day. It is typical for anxiety to cause symptoms to be more noticeable, and tremor (or shakiness) of the voice can be an associated feature. Those with SD often report that speaking with strangers, using the telephone, or public speaking makes the voice worse.
SD, like most dystonias, is task-specific - it is only evident during one type of activity. Other laryngeal actions, like breathing and swallowing, are usually unaffected. Sometimes, the voice will even be fluent while laughing or singing, but not during connected speech. This feature, combined with the deterioration of the voice with anxiety, occasionally causes the disorder to be mistakenly attributed to psychiatric causes. SD is not a psychiatric or psychological disease, but a true neurological one.
SD is a disorder of vocal fold movement, so the larynx has to be examined during voicing, and preferably during connected speech. The typical involuntary motions of the vocal folds are brief and spasm-like (hence the term “spasmodic”), and may occasionally be difficult to recognize. This is especially true if the examination is being performed with rigid endoscopy, which requires the tongue to be pulled forward. For this reason, flexible laryngoscopy through the nose is better than rigid laryngoscopy for diagnosis of SD.
Diagnosis of SD is made from a person’s description and demonstration of the problem, and from observation of the vocal folds during voicing. There is no specific finding on any test that identifies SD. Ultimately, the diagnosis is a matter of expert opinion.
There is no definitive cure for SD. Treatment is available to improve symptoms, and fortunately, that is almost always possible. It is important to understand that treatment only aims to improve symptoms, and that choosing not to get treated does not make the disease worse.
Laryngeal injections of botulinum toxin are the main therapy for SD. Voice therapy, psychological, psychiatric, and medical treatment alone have not proven useful in controlling SD symptoms.
Botulinum toxin has been used to treat SD since 1984. The principle behind treatment is to weaken the muscles that are behind the inappropriate motion. In the case of AdSD, these are the muscles that bring the vocal folds together, and in AbSD, the muscles that bring the vocal folds apart. The injection is performed through the skin of the neck as an office procedure. Afterwards, patients can usually go on with normal activities of their day.
Over the last 30 years, many surgeons have tried to treat SD by cutting or modifying the nerve supply to the larynx, or by altering the anatomy of the larynx. Early results have been encouraging, but, for complex reasons having to do with the brain abnormality underlying dystonia, the disorder can return. Most of these surgical procedures involve some degree of irreversible destruction of laryngeal function, and may remain unable to mitigate symptoms in the long-term. Currently, surgery is a second-choice treatment, best reserved for those in whom botulinum toxin injections are not possible or ineffective. Other invasive techniques, such as laryngeal stimulation implants, have been proposed to minimize the impact of SD symptoms, but they remain investigational at this time with no definitive evidence of effectiveness.