Abstract

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

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

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

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

Signs and symptoms

Symptoms of spasmodic dysphonia can come on suddenly or gradually appear over the span of years. They can come and go for hours or even weeks at a time, or remain consistent. Gradual onset can begin with the manifestation of a hoarse voice quality, which may later transform into a voice quality described as strained and breaks in phonation. These phonation breaks have been compared to stuttering in the past, but there is a lack of research in support of spasmodic dysphonia being classified as a fluency disorder. It is commonly reported by people with spasmodic dysphonia that symptoms almost only occur on vocal/speech sounds that require phonation. Symptoms are less likely to occur at rest, while whispering, and/or on speech sounds that do not require phonation. It is hypothesized this occurs because of an increase in sporadic, sudden, and prolonged tension found in the muscles around the larynx during phonation. This tension affects the abduction and adduction (opening and closing) of the vocal folds. Consequently, the vocal folds are unable to retain subglottal air pressure (required for phonation) and breaks in phonation can be heard throughout the speech of people with spasmodic dysphonia.

Regarding types of spasmodic dysphonia, the main characteristic of spasmodic dysphonia, breaks in phonation, is found along with other varying symptoms. The voice quality of adductor spasmodic dysphonia can be described as “strained-strangled” from tension in the glottal region. Voice quality for abductor spasmodic dysphonia can be described as breathy from variable widening of the glottal region. Vocal tremor may also be seen in spasmodic dysphonia. A mix and variance of these symptoms are found in mixed spasmodic dysphonia.

Symptoms of spasmodic dysphonia typically appear in middle aged people, but have also been seen in people in their twenties, with symptoms emerging as young as teenage years.

Cause

Although the exact cause of spasmodic dysphonia (i.e., laryngeal dystonia) is still unknown, epidemiological, genetic and neurological pathogenic factors have been proposed in recent research.

Risk factors include:

- Being female

- Being middle aged

- Having a family history of neurological diseases (e.g., tremor, dystonia, meningitis and other neurological diseases)

- Stressful events

- Upper respiratory tract infections

- Sinus and throat illnesses

- Heavy voice use

- Cervical dystonia

- Childhood measles or mumps

- Pregnancy and parturition

It has not been established whether these factors directly impact the development of spasmodic dysphonia (SD), however these factors could be used to identify possible and/or at-risk patients.

Researchers have also explored the possibility of a genetic component to SD. Three genes have been identified that may be related to the development of focal or segmental dystonia: TUBB4A, THAP1 and TOR1A genes. However, a recent study that examined the mutation of these three genes in 86 SD patients found that only 2.3% of the patients had novel/rare variants in THAP1 but none in TUBB4A and TOR1A. Evidence of a genetic contribution for dystonia involving the larynx is still weak and more research is needed in order to establish a causal relationship between SD and specific genes.

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.

SD is classified as a neurological disorder. 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. 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." 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". 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. The opinion that SD is psychogenic is not upheld by experts in the scientific community.

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

Diagnosis

Diagnosis of spasmodic dysphonia requires a multidisciplinary team and consideration of both perceptual and physiological factors. There is currently no universally accepted diagnostic test for spasmodic dysphonia, which presents a challenge for diagnosis. Additionally, diagnostic criteria have not been agreed upon as the distinguishing features of this disorder have not been well-characterized. Because spasmodic dysphonia shares many characteristics with other voice disorders, misdiagnosis frequently occurs. A common misdiagnosis is muscle tension dysphonia, a functional voice disorder which results from use of the voice, rather than a structural abnormality. Differential diagnosis is particularly important for determining appropriate interventions, as the type and cause of the disorder have an impact on the most effective treatment. Differences in treatment effectiveness are present even between the types of spasmodic dysphonia. Diagnosis of spasmodic dysphonia is often delayed due to these challenges, which in turn presents difficulties in choosing the proper interventions.

A team of professionals including a speech-language pathologist, an otolaryngologist, and a neurologist, is typically involved in spasmodic dysphonia assessment and diagnosis. The speech-language pathologist conducts a speech assessment including case history questions to gather information about voice use and symptoms. This is followed by clinical observation of voice characteristics such as voice breaks or strain, which are selectively present in normal speech over other voice activities such as whispering or laughing. Symptoms also vary across types of spasmodic dysphonia. For example, voiced sounds are more affected in adductor spasmodic dysphonia, while unvoiced sounds are more affected in abductor spasmodic dysphonia. Following speech assessment, the otolaryngologist conducts a transnasal laryngoscopy to view the vocal folds and activity of the muscles controlling them in order to eliminate other possible causes of the voice disorder. In spasmodic dysphonia, producing long vowels or speaking sentences results in muscle spasms which are not observed during other vocal activities such as coughing, breathing, or whispering. To evaluate the individual for any other neurological problems, this examination is followed up with an assessment by the neurologist.

Diagnosis | Types

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

Diagnosis | Types | 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. 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.

Diagnosis | Types | Abductor spasmodic dysphonia

In abductor spasmodic dysphonia, sudden involuntary muscle movements or spasms cause the vocal folds to open. 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.

Diagnosis | Types | 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.

Diagnosis | Types | 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). This gene encodes a tubulin gene. The pathophysiology of this condition has yet to be determined.

Treatment

There are a number of potential treatments for spasmodic dysphonia, including botox, surgery and voice therapy. 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.

Treatment | Voice therapy

Voice therapy appears to be ineffective in cases of true spasmodic dysphonia, however as it is difficult to distinguish between spasmodic dysphonia and functional dysphonias and misdiagnosis is relatively common, a trial of voice therapy is often recommended before more invasive procedures are tried. Some also state that it is useful for mild symptoms and as an add-on to botox therapy and others report success in more severe cases. Laryngeal manual therapy, which is massaging of the neck and cervical structures, also shows positive results for intervention of functional dysphonia.

Treatment | 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.

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. Post-surgery voices can be imperfect and about 15% of people have significant difficulties. If symptoms do recur this is typically in the first 12 months. Another operation called "recurrent laryngeal nerve avulsion" has positive outcomes of 80% at three years.

Another surgical option is a thyroplasty, which ultimately changes the position or length of the vocal folds. After thyroplasty there is an increase in both objective and subjective measures of speech.

Treatment | 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, 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.