Laryngeal dystonia (LD) is a chronic voice disorder characterized by momentary periods of uncontrolled spasms of the muscles of the voice box (larynx). These muscles control speech. The spasms can result in tightness in the throat, recurrent hoarseness, and changes in voice quality and/or difficulty speaking. At certain times, affected individuals must make a conscious effort in order to speak. The most frequent sign of this disorder is a sudden, momentary lapse or interruption of the voice. When affected individuals speak, their voice may sound strained, forced, strangled, breathy, or whispery. In severe cases, an affected individual may be barely able to speak. LD can potentially cause significant quality of life issues for affected individuals impacting both work and social situations. The disorder can cause psychological effects including depression and anxiety. There is no cure for LD, but the disorder can be effectively treated. The cause of LD is not known.
Laryngeal dystonia is a form of dystonia, a group of movement disorders that vary in their symptoms, causes, progression, and treatments. This group of conditions is generally characterized by involuntary muscle contractions that force the body in abnormal, sometimes painful, movements and positions (postures). LD is classified as a focal dystonia because it affects a specific part of the body (muscles within the voice box). LD is also known as spasmodic dysphonia.
The severity of LD can fluctuate from symptom-free periods with normal voice to severely disabling periods where an affected individual will experience significant difficulty speaking clearly or be barely able to speak. Symptom fluctuation can occur during the same day or from day to day or longer. LD tends to affect normal conversational speech. Several studies have shown that singing, laughing, yelling, etc. are usually unaffected by the disorder.
There are two main types of LD, adductor LD and abductor LD. Adductor LD, the more common type, affects approximately 80% to 90% of individuals. This type affects the muscles that draw the vocal cords together and the vocal cords sometimes become locked. Adductor LD is characterized by a tight, strained, or harsh sounding voice. Affected individuals may experience difficulties in the voicing of specific vowels sounds such as in the words “eat,” “back,” “I,” “olives,” or “nest”.
Abductor LD affects the muscles that draw the vocal cords apart. Abductor LD is characterized by breathy, whispered speech and loss of voice for short periods of time (aphonia). Individuals affected by the abductor type may have difficulty controlling speech after certain sounds (e.g., “h,” “s,” “p,” “t,” or “k”.
In some cases, affected individuals may exhibit both types, referred to as mixed LD. Some individuals also experience a vocal tremor, in which the larynx and vocal cords shake potentially affecting speech and making the voice difficult to understand because it sounds shaky or quivery.
Onset of LD is usually gradual and the initial symptoms may be mild. Symptoms may progress for the first 2-5 years then generally stabilize. Approximately 15% of patients progress into other forms of dystonia involving the face or neck. The disorder usually remains chronic without marked changes over a period of years, although symptoms may worsen with stress. The number and severity of symptoms varies widely among affected individuals.
The exact cause of LD is not known (idiopathic). Several different factors may be involved in the development of the disorder (multifactorial). Several theories exist that attempt to explain the underlying mechanisms of LD including abnormal functioning of portions of the brain involved in muscle control, or imbalances in neurotransmitters. Neurotransmitters are chemicals that modify, amplify, or transmit nerve impulses from one brain cell (neuron) to another, enabling nerve cells to communicate. Although the underlying mechanisms and causes of LD are not well understood, research is ongoing to determine the specific roles that genetic, environmental, and other factors ultimately play in the development of the disorder.
There are reports in the medical literature that suggest LD may develop following specific factors such as an upper respiratory infection or bronchitis, trauma or surgery, or exposure to certain drugs and/or toxins. However, such theories are controversial because there is no scientific evidence conclusively linking these factors to LD.
Genetic factors are believed to play a role in some cases, especially in individuals who have relative with another form of dystonia. These individuals may have a genetic susceptibility to developing the disorder. A person who is genetically predisposed to a disorder carries a gene (or genes) for the disease, but it may not be expressed unless it is triggered or activated by other genetic modifiers or environmental factors (complex genetics).
A specific genetic form of dysphonia, known as whispering dysphonia or DYT4 dystonia, has been identified in a large Australian family (kindred). This form of dysphonia is caused by mutations in the TUBB4 gene. Researchers have speculated that different mutations in this gene may contribute to the development of LD. More research is necessary to determine what role this or other genes have in the development of LD.
LD occurs more often in females than males and can affect individuals of all ethnic backgrounds. Onset can occur at any age, but usually occurs between 20 and 60 years of age. The exact incidence or prevalence of the disorder is unknown. LD is estimated to affect approximately 50,000 people in North America. However, determining the true frequency of LD in the general population is difficult because many cases are misdiagnosed or go undiagnosed.
The diagnosis of LD usually includes inspection of the voice box (laryngoscopy) to rule out structural abnormalities of the vocal cords such as nodules, polyps, or tumors. The diagnosis may require speech pathology, otolaryngology, and neurology consultations. Laryngeal electromyogram (EMG) and nuclear magnetic resonance imaging (NMRI) have been used to identify any associated neurological disorders.
There is no cure for LD. Treatment is aimed at the specific symptoms apparent in each individual. Psychological support and counseling can help individuals cope with depression, anxiety or other psychological issues associated with LD.
Botulinum toxin therapy is often used for LD. The drug works by weakening the muscle by blocking nerves impulses to the muscle and preventing the release of the neurotransmitter acetylcholine, which stimulates muscular contractions. The drug is injected into the vocal cords every three or four months, to reduce vocal cord spasms. Some individuals can wait longer between injections before symptoms return and more injections are needed. The degree of effectiveness of Botulinum toxin will differ in each individual case. Botulinum toxin is approved by the Food and Drug Administration (FDA) for cervical dystonia and blepharospasm and is widely used off label to treat all forms of dystonia. Botulinum toxin is manufactured by Allergan Pharmaceuticals (as BOTOX®), Elan Pharmaceuticals (as MYOBLOC®), Ipsen Pharmaceuticals (as DYSPORT®), and Merz Pharmaceuticals (as XEOMIN®).
Speech or voice therapy such as voice relaxation techniques may be beneficial for some individuals with LD, especially those with mild cases of the disorder. Speech or voice therapy may also be effective in treating side effects associated with other treatments such as Botulinum toxin (adjuvant therapy). Some individuals may benefit from using machines or devices that amplify the voice.
Oral medications have been used to treat forms of dystonia such as LD. However, there are no oral medications that are FDA approved for such use. Such medications include dopaminergic agents (levodopa), anticholinergic agents (benztropine, trihexyphenidy), baclofen, and clonazepam. These drugs act in various way to reduce muscle or nerve activity, but are often associated with adverse side effects.
If other therapeutic options are ineffective, contraindicated, or no longer effective after initially providing relief, then surgery may be recommended. Surgery may be aimed at separating the vocal cords or weakening the affected muscles of the larynx. Specific procedures include thyroplasty or selective laryngeal adductor denervation-reinnervation.
Decisions concerning the use of particular drug regimens and/or other treatments such as surgery should be made by physicians and other members of the health care team in careful consultation with parents or a patient based upon the specifics of an individual case; a thorough discussion of the potential benefits and risks, including possible side effects and long-term effects; patient preference; and other appropriate factors.
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