Spasmodic dysphonia

Spasmodic dysphonia, also known as laryngeal dystonia, is a disorder in which the muscles that generate a persons voice go into periods of spasm.^[1][2] This results in breaks or interruptions in the voice, often every few sentences, which can make a person difficult to understand.^[1] The person's voice may also sound strained or they may be nearly unable to speak.^[2] Often onset is gradual and the condition is life long.^[1]

The cause is unknown.^[1] Risk factors may include family history.^[1] Triggers may include an upper respiratory infection, injury to the larynx, overuse of the voice, and psychological stress.^[1] The underlying mechanism is believed to typically involve the central nervous system, specifically the basal ganglia.^[1] Diagnosis is typically made following examination by a team of healthcare providers.^[1]

While there is no cure, treatment may improve symptoms.^[1] Most commonly this involves injecting botulinum toxin into the affected muscles of the larynx.^[1] This generally results in improvement for a few months.^[1] Other measures include voice therapy, counselling, and amplification devices.^[1] Rarely surgery may be considered.^[1]

The disorder affects an estimated 2 per 100,000 people.^[1] Women are more commonly affected.^[1] Onset is typically between the ages of 30 and 50.^[1] Severity is variable between people.^[2] In some work and social life are affected.^[2] Life expectancy is, however, normal.^[3]

Types

The three types of spasmodic dysphonia (SD) are adductor spasmodic dysphonia, abductor spasmodic dysphonia and mixed spasmodic dysphonia.

Adductor spasmodic dysphonia

In adductor spasmodic dysphonia (ADSD), sudden involuntary muscle movements or spasms cause the vocal folds (or vocal cords) to slam together and stiffen.^[4] These spasms make it difficult for the vocal folds to vibrate and produce voice. Words are often cut off or are difficult to start because of the muscle spasms. Therefore, speech may be choppy but differs from stuttering. The voice of an individual with adductor spasmodic dysphonia is commonly described as strained or strangled and full of effort. Surprisingly, the spasms are usually absent while laughing, speaking at a high pitch, or speaking while singing, but singers can experience a loss of range or the inability to produce certain notes of a scale or with projection. Stress, however, often makes the muscle spasms more severe.^[5]

Abductor spasmodic dysphonia

In abductor spasmodic dysphonia, sudden involuntary muscle movements or spasms cause the vocal folds to open.^[4] The vocal folds cannot vibrate when they are open. The open position of the vocal folds also allows air to escape from the lungs during speech. As a result, the voices of these individuals often sound weak, quiet and breathy or whispery. As with adductor spasmodic dysphonia, the spasms are often absent during activities such as laughing or singing, but singers can experience a loss of range or the inability to produce certain notes of a scale or with projection.^[5]

Mixed spasmodic dysphonia

Mixed spasmodic dysphonia involves both muscles that open the vocal folds and those that close them and therefore has features of both adductor and abductor spasmodic dysphonia.^[4]

Whispering dysphonia

A fourth type has also been described. This appears to be caused by mutations in the TUBB4 gene on the short arm of chromosome 19 (19p13.2-p13.3).^[6] This gene encodes a tubulin gene. The pathophysiology of this condition has yet to be determined.

Cause

The exact cause of spasmodic dysphonia (SD) is unknown.^[4] Evidence is that most cases are in neurogenic or having to do with the nervous system.^[5]

SD is a neurological disorder rather than a disorder of the larynx, and as in other forms of dystonia, interventions at the end organ (i.e., larynx) have not offered a definitive cure, only symptomatic relief. The pathophysiology underlying dystonia is becoming better understood as a result of discoveries about genetically based forms of the disorder, and this approach is the most promising avenue to a long-term solution.^[7]

SD is classified as a neurological disorder.^[8] However, because the voice can sound normal or near normal at times, some practitioners believe it to be psychogenic, that is, originating in the affected person's mind rather than from a physical cause. No medical organizations or groups take this position. A comparison of SD patients compared with vocal fold paralysis (VFP) patients found that 41.7% of the SD patients met the DSM-IV criteria for psychiatric comorbidity compared with 19.5% of the VFP group.^[9] However, another study found the opposite, with SD patients having significantly less psychiatric comorbidity compared to VFP patients: "The prevalence of major psychiatric cases varied considerably among the groups, from a low of seven percent (1/14) for spasmodic dysphonia, to 29.4 percent (5/17) for functional dysphonia, to a high of 63.6 percent (7/11) for vocal cord paralysis."^[10] A review in the journal Swiss Medicine Weekly states that "Psychogenic causes, a 'psychological disequilibrium', and an increased tension of the laryngeal muscles are presumed to be one end of the spectrum of possible factors leading to the development of the disorder".^[11] Alternatively, many investigators into the condition feel that the psychiatric comorbidity associated with voice disorders is a result of the social isolation and anxiety that patients with these conditions feel as a consequence of their difficulty with speech, as opposed to the cause of their dysphonia.^[12] The opinion that SD is psychogenic is not upheld by experts in the scientific community.^[10][13]

SD is formally classified as a movement disorder, one of the focal dystonias, and is also known as laryngeal dystonia.^[14]

Diagnosis

Diagnosis of spasmodic dysphonia is often delayed due to lack of recognition of its symptoms by screening physicians. Most people who are correctly diagnosed are evaluated by a team that usually includes an otolaryngologist, a speech-language pathologist and a neurologist. The otolaryngologist examines the vocal folds using a ridged or flexible (transnasal) laryngoscopy to look for other possible causes for the voice disorder. Fiberoptic laryngoscopy, a method whereby a small lighted flexible tube is passed through the nose and into the throat, is a helpful tool that allows the evaluation of the vocal cords movement during speech. Additional diagnostic testing may include stroboscopy, which allows the viewing of the vibrations of the vocal cords in slow motion. The speech-language pathologist evaluates the patient's voice and voice quality. The neurologist evaluates the person for signs of other movement disorders.^[5]

Treatment

There are a number of potential treatments for spasmodic dysphonia, including botox, surgery and voice therapy.^[15] A number of medications have also been tried including anticholinergics (such as benztropine) which have been found to be effective in 40-50% of people, but which are associated with a number of side effects.^[16]

Voice therapy

Voice therapy appears to be ineffective in cases of true spasmodic dysphonia,^[17] however as it is difficult to distinguish between spasmodic dysphonia and functional dysphonias and misdiagnosis is relatively common,^[18] a trial of voice therapy is often recommended before more invasive procedures are tried.^[15] Some also state that it is useful for mild symptoms and as an add-on to botox therapy^[19] and others report success in more severe cases.^[20]

Surgery

A number of operations that cut one of the nerves of the vocal folds (the recurrent laryngeal nerve) has improved the voice of many for several months to several years but the improvement may be temporary.^[5]

An operation called "selective laryngeal adductor denervation-rennervation (SLAD-R)" is effective specifically for adductor spasmodic dysphonia which has shown good outcomes in about 80% of people at 8 years.^[17] Post-surgery voices can be imperfect and about 15% of people have significant difficulties.^[17] If symptoms do recur this is typically in the first 12 months.^[17] Another operation called "recurrent laryngeal nerve avulsion" has positive outcomes of 80% at three years.^[19]

Botulinum toxin

Botulinum toxin (Botox) is often used to improve some symptoms of spasmodic dysphonia. Whilst the level of evidence for its use is limited,^[21] it remains a popular choice for many patients due to the predictability and low chance of long term side effects. It results in periods of some improvement. The duration of benefit averages 10–12 weeks before the patient returns to baseline. Repeat injection is required to sustain good vocal production.^[15]

Notable cases

• Scott Adams, the creator of the comic strip Dilbert.^[22]
• Frank Allison, musician, leader of Frank Allison and the Odd Sox^[23]
• Johnny Bush, country and western musician and songwriter^[24]
• Keath Fraser, Canadian author who has documented the challenges and treatment of his condition in the book The Voice Gallery: Travels With a Glass Throat (2002).^[25]
• Susan Collins, Senior United States Republican Senator from Maine ^[26]
• Chip Hanauer, American hydroplane racing driver^[27]
• Robert F. Kennedy, Jr., political and environmental activist, son of Robert F. Kennedy^[28]
• Emily Lim, award-winning author of children's picture books.^[29]
• Mary Lou Lord, indie folk musician.^[30]
• Darryl McDaniels of the rap group Run DMC.^[31]
• Lianne Morgan, singer/songwriter, in the first line up of the Spice Girls.^[32]
• Jenny Morris (OAM), a New Zealand-born Australian pop, rock singer-songwriter.^[33][34]
• Diane Rehm, host of The Diane Rehm Show on National Public Radio (NPR).^[35]
• Jimmie Rodgers, American pop musician, best known for his version of "Kisses Sweeter than Wine."^[36]
• Mark Stuart, American Christian rock musician (formerly of Audio Adrenaline)^[37]
• Linda Thompson, British folk-rock musician.^[38]
• Shania Twain, country music recording artist and songwriter.^[39]

References