Spasmodic Dysphonia

Traube, who believed the condition to be a form of nervous hoarseness, first described spasmodic dysphonia (SD) in 1871. ^[2] For many years, the disorder was referred to as spastic dysphonia, but the term spasmodic dysphonia is more widely accepted today.

Dedo first introduced recurrent laryngeal nerve section for the treatment of spasmodic dysphonia (SD) in 1976. ^[3] Other investigators modified this approach by crushing the recurrent laryngeal nerve. ^[4] However, the use of these techniques gradually declined because of a high late recurrence rate and the inherent disability that occurred. ^[5]

In 1980, Isshiki et al introduced a laryngeal framework surgery (laryngoplasty) for patients with adductor spasmodic dysphonia (SD). ^[6] This technique permits adjustment of the position and tension in the vocal folds. This surgical approach is still experimental, and further investigation is required.

Blitzer et al applied the botulinum toxin injection technique in 1984. ^[7] This procedure has become the treatment of choice for spasmodic dysphonia (SD). Advantages of this technique include a high success rate in restoring or improving the voice. However, botulinum toxin injections provide only temporary symptomatic relief, and repeated intramuscular injections are required.

Recent surgical advances include recurrent laryngeal nerve denervation and reinnervation, as well as thyroarytenoid (TA) and lateral cricoarytenoid myectomy. These procedures have not yet been widely accepted as a primary treatment for spasmodic dysphonia (SD), and their long-term efficacy is controversial. ^{[8, 9]}

Frequency

Early textbooks reported that spasmodic dysphonia (SD) was a relatively rare voice disorder, although recent reports suggest that it is not rare but rather frequently goes undiagnosed. Most studies show that this disorder affects females more commonly than males, with a female-to-male ratio as high as 4:1. ^[10]

Reports of the mean age of patients with spasmodic dysphonia (SD) typically indicate a range of 39-45 years; however, the condition may occur as early as the second decade of life in rare exceptions and as late as the ninth decade of life. ^{[10, 11]}

Although a genetic basis of spasmodic dysphonia (SD) has not been established, some patients (12%) report relatives with similar voice problems or other dystonias. ^[11]

The origin of spasmodic dysphonia (SD) is currently unknown. Primary generalized dystonia is clearly a genetic disorder and has been attributed to a defect on bands 9q32-34. ^[12] The location of the genetic defect in patients with primary focal dystonias is unknown.

Hall et al described a case in which spasmodic dysphonia (SD) was associated with hereditary spastic paraplegia type 7 (SPG7 mutation). ^[13]

Spasmodic dysphonia (SD) is currently understood to be a focal dystonia that affects laryngeal muscle control during speech. Dystonia refers to a syndrome of sustained muscle contractions. Focal dystonias involve abnormal activity in only a few muscles. Dystonic movements are aggravated or become manifest during voluntary movement and worsen with fatigue or physical and emotional stress. Dystonia may be focal, segmental, multifocal, or generalized. Although spasmodic dysphonia (SD) is considered a focal dystonia, it may present as a segmental or multifocal dystonia.

Spasmodic dysphonia (SD), as with other neuromotor disorders, is frequently associated with tremor. Essential tremor causes 6- to 8-Hz shaking, primarily of the hands, head, and voice. In spasmodic dysphonia (SD), the tremor may be isolated to the larynx or may involve the pharynx, head, or even hands.

The preponderance of evidence suggests that idiopathic dystonias are due to an abnormality of neurotransmitters in the basal ganglia (putamen, head of caudate, and upper brainstem). Zweig et al suggested that the putamen and the striatopallidothalamocortical circuit are disrupted in patients with focal dystonias. ^[14]

A study by Khosravani et al using electroencephalographic analysis indicated that compared with healthy controls, persons with spasmodic dysphonia (SD) demonstrate, during voice production, “a reduced movement-related desynchronization of motor cortical networks” and “an excessively large synchronization between left somatosensory and premotor cortical areas.” ^[15]

A study by Simonyan et al suggests that the pathophysiology of spasmodic dysphonia (SD) may be related to specific brain abnormalities. ^[16] Evidence from both diffusion tensing imaging and neuropathological data show specific white matter changes along the corticobulbar and corticospinal tracts and in the brain regions contributing to them. Specifically, the genu of the internal capsule was found to have decreased quality and density of axonal tracts.

Postmortem histopathology also confirmed reduced axonal course and myelin content in the right genu of the internal capsule. An increase in microglial activation in these regions suggests a slow demyelination process. The changes in the CBT/CST suggest deficiency in connection between the cortical and subcortical regions, which are essential for voluntary voice production. Diffusion tensor imaging found changes in the common areas sited for focal dystonias namely the basal ganglia, cerebellum, and thalamus. Postmortem clusters of mineral accumulations in these areas may suggest a pathological process that is common to focal dystonias. ^[16]

Similarly, Ali et al used H₂¹⁵O positron emission tomography (PET) scanning to examine speech-related changes in regional cerebral blood flow to assess patients both before and after botulinum toxin injection. ^[17] Their data demonstrate definitive patterns of cerebral activity in patients with adductor spasmodic dysphonia (SD) and neurologically normal controls. Their results suggest that the pathophysiology of spasmodic dysphonia (SD) is related to sensory cortical areas as well as motor areas.

Using PET imaging, activity in the postcentral gyrus, inferior parietal lobule, and middle temporal gyrus are found to be significantly reduced in patients with adductor spasmodic dysphonia (SD). Afferent (proprioceptive/tactile) feedback mechanisms that are controlled in these sensory areas are known to play a crucial role in coordinated oral-laryngeal movements. Hypoactivity suggests that this sensory feedback is not being processed appropriately in adductor SD. Without sensory feedback, intracortical inhibitory mechanisms are deficient.

Interestingly, botulinum toxin therapy resulted in a reversal of sensory hypoactivity 3-4 weeks after injection. The authors suggest that this process of renewed sensory feedback can lead to reorganization in both sensory and motor areas. Motor regions as well as the lateral premotor system (responsible for organizing and executing movements in response to afferent signals) are found to have an increase in cerebral blood flow. This suggests more efficient processing of sensory signals and possibly a return of normal inhibition. This may translate to clinical improvement in speech and voice after botulinum toxin injection. ^[17]

Using the Newcastle Laryngeal Hypersensitivity Questionnaire, a study by Vanderaa and Vinney reported that adductor spasmodic dysphonia (SD) and mixed (adductor/abductor) SD are significantly associated with laryngeal hypersensitivity. In addition, the study indicated that upper respiratory infection at the onset of SD is associated with greater severity of laryngeal hypersensitivity symptoms. The investigators stated that laryngeal sensory symptoms may play a role in or arise from SD motor spasms and/or have pathophysiologic implications in SD. ^[18]

The etiology of spasmodic dysphonia (SD) is unclear. Approximately half the patients can associate the onset if their symptoms with either an upper respiratory infection (30%) or a major life stressor (21%). ^[10] A study of 350 patients with spasmodic dysphonia showed that 35% of them could identify inciting events that caused the onset of their disorder, with 45% of these noting a sudden onset of dysphonia. The most commonly cited behavioral and environmental factors surrounding the onset of this disorder were stress, upper respiratory tract infections, and pregnancy/parturition. ^[19]

Adductor spasmodic dysphonia

Speech is characterized by strained or strangled phonation with intermittent voice offsets on voicing of vowels. Patients report that symptoms are worse when they are under emotional stress, when they talk on the telephone, or when they speak publically. The symptoms are often better upon awakening in the morning or after a drink of alcohol. Patients are generally able to whisper or sing without strain or vocal breaks; this is often not the case with muscle tension dysphonia and helps to clinically distinguish between the 2 disorders. Voicing is effortful, with strain and occasional hoarseness, but the essential symptom is voice breaks. The voice breaks are due to spasmodic hyperadductions of the folds that interrupt phonation. Upon fiberoptic laryngoscopy examination, the vocal folds of patients with adductor spasmodic dysphonia (SD) have intermittent rapid shortening and squeezing, which results in a quick glottic closure that shuts the glottis and interrupts airflow through the glottis.

Abductor spasmodic dysphonia

Abductor spasmodic dysphonia (SD) is rarer than the adductor type (17% of all patients with spasmodic dysphonia). ^[11] Patients have prolonged voiceless consonants because of difficulties with voice onset following voiceless sounds such as /h/, /s/, /f/, /p/, /t/, and /k/. Additional symptoms in some patients with abductor spasmodic dysphonia (SD) include pitch changes, phonatory breaks during vowels, uncontrolled rises in vowels' fundamental frequency, or a breathy voice quality. Upon fiberoptic laryngoscopy, patients with abductor spasmodic dysphonia (SD) have wide-ranging abduction movements for voiceless consonants that are prolonged and interfere with following vowels.

A careful evaluation of the patient by a multidisciplinary team is needed before the best treatment for that patient can be selected. The primary treatment modality as endorsed by the American Academy of Otolaryngology- Head and Neck Surgery is currently botulinum toxin injection into the laryngeal musculature. The patient should be counseled about the advantages and disadvantages of each management approach and their expected results.

The following treatment options are currently available:

• Botulinum toxin muscle injection

• Type II laryngoplasty

• Voice therapy

• Recurrent laryngeal nerve denervation and reinnervation

• TA and lateral cricoarytenoid myectomy

• Oral medical therapy

Contraindications and relative contraindications to botulinum toxin therapy are as follows:

• Pregnancy: Use of botulinum toxin by women who are pregnant or lactating is not recommended.

• Aminoglycosides: Recent use of aminoglycosides interferes with neuromuscular transmission and may increase the effect of the botulinum toxin therapy. The authors recommend that patients receiving aminoglycoside treatment not receive concurrent botulinum toxin injections.

• Gastroesophageal reflux: Administer antireflux therapy in patients with known or suspected reflux before considering botulinum toxin injections. Botulinum toxin injections reduce the speed of vocal fold closure and may predispose the patient to aspiration.

• Preexisting neurologic disorders (eg, myasthenia gravis, Eaton-Lambert syndrome, motor neuron disease affecting the neuromuscular junction): Use caution when administering botulinum toxin to patients with these disorders, especially when large doses are required. Although the amount of toxin that enters the systemic circulation after injection is minute, hyperkinetic symptoms could theoretically occur.