- 1 Types
- 2 Cause
- 3 Diagnosis
- 4 Treatment
- 5 Notable cases
- 6 References
- 7 External links
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. 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.
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.
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.
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.
The exact cause of spasmodic dysphonia (SD) is unknown. According to the National Institute on Deafness and Other Communication Disorders, "research has revealed increasing evidence that most cases of spasmodic dysphonia are in fact neurogenic or having to do with the nervous system (brain and nerves)."
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.
The National Institute of Neurological Disorders and Stroke (NINDS) and the American Academy of Neurology (AAN) classify SD 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.
Evidence for a neurological basis
SD is formally classified as a movement disorder, one of the focal dystonias, and is also known as laryngeal dystonia. Supporting evidence that SD is a neurological disorder includes:
- Affected Brain Regions: SD may co-occur with other neurological movement disorders such as blepharospasm (excessive eye blinking and involuntary forced eye closure), tardive dyskinesia (involuntary and repetitious movement of muscles of the face, tongue, body, arms and legs), oromandibular dystonia (involuntary movements of the jaw muscles, lips and tongue), torticollis (involuntary movements of the neck muscles), or tremor (rhythmic, quivering muscle movements). Diffusion tensor imaging has been used to identify brain differences between SD patients and healthy individuals and to target those brain regions for neuropathological examination in SD patients. The location of these brain abnormalities makes them specific to SD; they are located in the corticobulbar/corticospinal tract and its main input/output structures (the basal ganglia, thalamus, and cerebellum). It is suggested that SD may be associated with alterations in connectivity of the corticobulbar tract coming from the laryngeal/orofacial motor cortex to the brainstem phonatory nuclei. The basal ganglia balances excitation and inhibition of the thalamo-cortical circuit involved in motor execution; this balance is thought to be altered in task-specific dystonias due to reduced GABAergic metabolism and dopaminergic receptor binding—this leads to excessive motor cortical excitation. The cerebellum is involved in motor control via the ventrolateral thalamus and has a modulatory role in coordination of voice and speech production; cerebellar dysfunction and atrophy have been reported in a group of patients with dystonia, suggesting that this disorder may arise from cerebellar disorganization. Together these affected brain regions result in problems in linguistic output.
- Brainstem Pathology in Spasmodic Dysphonia: Spasmodic dysphonia runs in some families and is thought to be inherited. Research has identified a possible gene on chromosome 9 that may contribute to the spasmodic dysphonia that is common to certain families. Studies that have examined postmortem brainstem tissue from SD patients have found a presence of small clusters of microglia/macrophages activation in the reticular formation surrounding the lower brainstem nuclei involved in the control of laryngeal functions and mild neuronal degeneration and depigmentation in the substantia nigra and the locus coeruleus in SD patients compared to controls. The presence of small clusters of microglia/macrophages activation in the brainstem reticular formation of SD patients may represent a disorder-specific neuropathological process, because of their location in the area of the nuclei responsible for sensory (solitary tract and spinal trigeminal nuclei) and motor (nucleus ambiguus) control of voice production. Mild neuronal degeneration and depigmentation of the pars compact of the substantia nigra and the locus coeruleus is also similar to those reported in patients with idiopathic cervical dystonia, Meige’s syndrome and torsion dystonia. So the involvement of the substantia nigra and the locus coeruleus may represent a common neuropathogenic process in both early- and late-onset primary dystopias.
- Abnormal Structure–Function Relationship in Spasmodic Dysphonia: Histological examination of the nerve to the vocal cords in patients with SD demonstrates that the percentage of abnormally thin nerve fibers was higher than in normal controls In studies that have measured grey matter volume and cortical thickness and examined the measures for relationships with blood oxygen level-dependent signal change during speech production, it has been found that the left anterior insula in SD patients has decreased cortical thickness. Yet this part of the insula also has been found to have increased functional activation, positive relationships between cortical thickness measurements/brain activation, and SD symptom severity with no volumetric changes.The insula is involved in a wide variety of behaviors, including voice and speech control. This is due in part to its direct connections with the laryngeal motor cortex, inferior frontal gyrus, auditory, and cingulate cortexes. While several studies have suggested that it is involved in motor planning of speech production, this view also associates the anterior insula with the temporal processing of auditory stimuli and the control of automatic aspects of speech production.
- Abnormal Activation of the Primary Somatosensory Cortex in Spasmodic Dysphonia: Functional magnetic resonance imaging signal is reduced in sensorimotor cortices associated with movement of the affected body part in laryngeal dystonia, supporting a dystonic basis for this voice disorder. In fMRI studies that have aimed to identify symptom-specific functional brain activation abnormalities in SD, it has been found that increased activation intensity in SD patients was found only in the primary somatosensory cortex during symptomatic voice production. This suggests that abnormally increased extent and intensity of activation in this region may represent a disorder-specific phenomenon. Despite increased activation extent in the sensorimotor cortex in SD patients, some studies have found a lack of correlation in brain activation intensity between the primary motor and somatosensory cortices, which points to an impaired link between these two regions. As the sensory system plays an important role in driving the motor system, abnormal functional activation and correlations of the primary somatosensory cortex with other brain regions in SD patients may reflect the altered processing of sensory feedback, which, in turn, may affect motor control and sensorimotor functional integration during voice production in these patients.
Diagnosis of spasmodic dysphonia is often delayed due to lack of recognition of its symptoms by screening physicians. Most patients 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 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 otolaryngologist to evaluate vocal cord movement during speech. Additional diagnostic testing may include stroboscopy, which allows the physician to view 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 patient for signs of other movement disorders.
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.
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.
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.
Botulinum toxin (Botox)
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.
Neuroplasticity based re-education
Since the root of the problem is neurological, doctors have explored sensorimotor retraining activities to enable the brain to "rewire" itself and eliminate dystonic movements. The work of Joaquin Farias has shown that sensorimotor retraining activities and proprioceptive stimulation can induce neuroplasticity, making it possible for patients to recover substantial function that was lost due to Dysphonia.
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