Dystonia is defined as a state of anomalous muscular tonicity. The abnormal tonicity can result in a movement disorder that can affect a single muscle group or the entire body. Dystonia is typically characterized by sustained muscular contraction that is forceful and inappropriate. The affected individual may suffer from bizarre twisting, repetitive movements or abnormal postures. Although dystonia has been linked to malfunction in certain areas of the brain, such as the basal ganglia, the precise etiology remains unknown. It was previously thought that dystonia may be caused by a psychiatric disturbance. Recent studies, however, suggest that the emotional symptoms often experienced by affected individuals are caused by the disabling dystonia, and not vice versa.
Dystonias are generally classified into two groups, generalized and focal. Generalized (non-focal) dystonia involves a large number of muscle groups. Focal dystonia involves a single muscle group. Dystonia, whether generalized or focal, may be primary (idiopathic) or secondary to birth injury, hypoxia, infection (encephalitis/meningitis), toxic (drugs), or stroke.
The most common types of focal dystonia are blepharospasm, torticollis, writer’s cramp, and laryngeal. Laryngeal dystonia, also called spasmodic dysphonia, is a focal, primary dystonia, affecting the muscles of the larynx.
SPASMODIC DYSPHONIA (Focal Laryngeal Dystonia)
Spasmodic dysphonia (SD) is an extremely disabling form of dystonia that is often misdiagnosed. In a patient based survey conducted by the National Spasmodic Dysphonia association (1992), patients consulted an average of 4, and as many as 25 physicians before a correct diagnosis was made. The mean time to reach that correct diagnosis was 5 years. Only 4% of patients’ primary care physicians made a correct diagnosis. Individuals, on the average, traveled 160 miles to receive the appropriate treatment. These results highlight the difficulty that patients with SD experience before receiving the appropriate care.
Patients with SD have severely diminished vocal capacity. The voice can range from strangled and pressed to breathy and barely perceptible. The disorder is severely disabling, as 71% of patients with SD have a reduced social life and 25% can not work because of their condition.
CLASSIFICATION OF SD
There are several different types of SD. Successful treatment relies upon accurately identifying the muscles involved so that they can be appropriately targeted during treatment. Koufman (1996) classified SD into 3 main categories. These groups include adductor, abductor, and mixed.
Adductor type SD: An adductor is a muscle that draws a part of the body toward the median plane. In the larynx, the median plane is the midline of the airway. Thus, laryngeal adductors close the vocal folds. Adductor SD is the most common type of SD. It is responsible for over 80% of all focal laryngeal dystonias. It is characterized by inappropriate and sustained overclosure of the vocal folds during phonation. The voice typically takes on a strained, staccato-like quality with multiple voice breaks during connected speech. Patients may resort to whispering, and may attempt to speak on exhalation as well as inhalation. The voice may become worse during times of stress and may actually improve when the individual is surprised, scared, angry or intoxicated, or during singing and laughing. Clinically, the voice specialist observes bilateral co-contractions of the vocalis/thyroarytenoid muscles which appear to be worse with vowel initiated words. This type of SD can be further subclassified into glottic and supraglottic types with or without tremor depending upon the degree of endolaryngeal (true and false vocal folds, epiglottis, aryepiglottic folds) involvement. Typically, the more supraglottic involvement, the worse the dystonia.
Abductor type SD: An abductor is a muscle that draws a part of the body away from the median plane. In the larynx, only one muscle is responsible for abduction, or opening of the vocal folds – the posterior cricoarytenoid (PCA) muscle. Pure abductor SD is responsible for 4% of all focal laryngeal dystonias. It is characterized by forceful and sustained contractions of the PCA muscles. Thus, patients with abductor SD have sustained and inappropriate hyper-abductions (forced openings) of the vocal folds. This results in severe air wasting, breathy dystonia, and distorted vocal fluency.
Mixed type SD: Responsible for 11% of all focal laryngeal dystonias. Mixed dystonias usually result from the development of compensatory maneuvers. This may only become apparent after the primary dystonia has been treated. Treatment of mixed type SD is complex and may require several different treatment modalities.
Dystonia tremor: Tremor may be a component of either adductor or abductor type SD. Pure dystonia tremor (Koufman, 1996), is a variant of adductor type SD. In comparison to essential tremor that is present throughout the entire respiratory cycle, dystonia tremor is present only during phonation. Tremor in conjunction with SD does respond to therapy, although treatment is generally more difficult and somewhat less effective.
Non-focal laryngeal dystonia: Dystonia affecting the larynx as well as other groups of muscles. This may be seen in patients with encephalitis, Meige’s syndrome (oromandibular dystonia), Leigh syndrome, cerebellar infarct, and cerebral palsy. Treatment is targeted at the particular groups of affected muscles.
TREATMENT OF SD
The treatment for SD involves weakening the spastic muscles so that the inappropriate hyper-adductions or hyper-abductions may be reduced. This can be done surgical through a variety of techniques, or medically, with the use of botox.
Botulinum toxin is the most toxic natural substance known to man. It is an exotoxin of the organism Clostridium botulinum. Botulinum toxin is the cause of botulism, a disorder caused by intoxication with spoiled food that leads to weakness of skeletal muscle including the muscles of respiration. Botulinum toxin exerts its effect by blocking the release of the neurotransmitter acetylcholine. The toxin was originally investigated by the military for use in its biologic warfare program. It was first used therapeutically in the early 1980’s to treat blepharospasm, a disorder characterized by an involuntary squinting of the eyes. Botulinum toxin type A (BOTOX®) has been used in the management of SD since the late 1980s. It works by temporarily weakening dystonic laryngeal muscles, thereby allowing for a more normal speech. Minute quantities are injected into the involved muscles (thyroarytenoid muscles for adductor and PCA muscles for abductor SD). Because the toxin wears off over time, repeat injections are usually necessary. Normal or near normal voice may be achieved for 2 to 6 months. A brief period (1-2 weeks) of breathy voice may precede the vocal improvement. Swallowing problems and breathing difficulty may occur after an injection, although this complication is very rare and resolves with time. The exact dose of Botox injected is tailored to the individual needs of the patient. A couple of injections may be necessary to “titrate” the most efficacious dose for each person.
B. SURGICAL TREATMENTS FOR SD
Several surgical treatments for SD have been devised over the past several years. They are all targeted at mechanically denervating or surgically weakening the involved muscles. The recurrent laryngeal nerve (RLN) is the nerve that innervates all of the muscles to the larynx except one (cricothyroid). Dedo (1976) sectioned (cut) the RLN in patients with SD and reported a significant improvement in vocal quality. The initial success after RLN section, however, was transient, as the SD recurred in many of the treated patients. RLN section is seldom practiced today.
Thyroarytenoid myectomy has recently been introduced as a potential treatment for SD. It may be done through an external (neck incision) or endoscopic (per oral or through the mouth) approach. The technique involves mechanically weakening the involved muscles with either the CO2 laser or surgical forceps. Among patients with adductor SD, the targeted muscle is the thyroarytenoid muscle. Among patients with abductor SD, the targeted muscle is the posterior cricoarytenoid (PCA) muscle. This technique has achieved some promising results in a select group of SD patients. Further research is needed in order to evaluate long-term efficacy.
Another surgical procedure has recently been developed for adductor SD whereby the adductor branch of the recurrent laryngeal nerve is cut bilaterally, and the distal nerve stumps are reinnervated with branches of the ansa cervicalis nerve. Although initial reports of success with this procedure have been promising, follow-up is needed to evaluate long-term efficacy.
Medialization laryngoplasty is a technique in which small implants are placed lateral to the thyroarytenoid muscles in order to improve glottal closure. Several materials may be utilized. These include autologous fat, collagen, silastic (surgical grade plastic), and Gore Tex. Among patients with abductor SD, medialization laryngoplasty has displayed some success in improving vocal quality. Botox injections may still be needed. Some patients with SD also have glottal insufficiency (bowing of the vocal folds). This is usually due to atrophy from the natural aging process. Patients with SD and vocal fold bowing may actually get worse with Botox. After chemically weakening the vocal folds with Botox, closure of the bowed vocal folds is inadequate to achieve normal voicing. Thus, even in patients with adductor SD, medialization laryngoplasty may be utilized to address the bowing. Botox is then used to treat the SD.
Spasmodic dysphonia, also called focal laryngeal dystonia, is a voice disorder that can be disabling and difficult to diagnose. Depending on the affected laryngeal muscles, SD can be classified as adductor type, abductor type, and mixed type dystonia. Tremor may accompany any type of SD and can make treatment more difficult.
Our approach to the patient with SD at the Center for Voice and Swallowing at UC Davis involves an individualized treatment protocol. SD, like many voice disorders, may be complex and involve more than one diagnosis. For example, a patient with SD may also have presbylaryngis and laryngopharyngeal reflux. A patient previously diagnosed with adductor SD may actually suffer from a mixed dystonia. Among patients with SD, as in all patients with voice disorders presenting to the UC Davis Center for Voice and Swallowing, we maintain a high index of suspicion for secondary diagnoses and tailor individual therapy accordingly.
The gold standard therapy for SD remains treatment with Botox. Injections are safe, effective, very well tolerated, and take less than 5 minutes to perform. The frequency and dose of Botox injected depends on several patient factors including age, weight, anatomy, and vocal requirements of the individual patient. In persons with particular needs, an aversion to Botox, or poor results with standard therapy, we employ one of the many available surgical options.