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Phillip C. Song, R. Lucian Sulica, Daniel Fink,
and Tanya K. Meyer

Spasmodic dysphonia is a clinical syndrome characterized by involuntary, hyperfunctional spasms or postures of the internal laryngeal musculature, producing abnormal speech. Traube1 first used the term spastic dysphonia to describe patients with nervous hoarseness in 1871. Historically, the terms spastic dysphonia, aspartic aphonia, phonic laryngeal spasm, and coordinated laryngeal spasm have been used to describe the same clinical presentation.^2,3 Long thought to be psychological, spasmodic dysphonia was shown to be clearly organic and neurologic in nature by the dramatic response to nerve section in pioneering work by Dedo and Behlau.⁴ In 1982, Mard sen and Sheehy⁵ recognized the underlying pathology to be dystonia. They noted that “all evidence points to the conclusion that blepharospasm and oromandibular dystonia seen in Meige disease is another manifestation of adult-onset torsion dystonia, [and] since dysphonia may occur in the same syndrome, it is quite likely that dysphonia itself may be the sole manifestation of dystonia.” In 1988, Blitzer and colleagues⁶ used clinical examination and laryngeal electromyography to prove that most cases of spastic dysphonia actually represented focal cranial dystonias.

Spasmodic dysphonia is classified as a laryngeal dystonia, a clinical term used to describe an action-induced, task-specific, laryngeal neuromuscular disorder.7 Dystonias are classified by clinical symptom, age at onset, distribution, and cause. When classified by distribution, dystonias are categorized as focal, segmental, multifocal, or generalized. Spasmodic dysphonia is a focal dystonia involving the laryngeal adductor muscles (lateral cricoarytenoid, interarytenoid, thyroarytenoid, and possibly the cricothyroid), abductor muscles (posterior cricoarytenoid), or both, with occasional involvement of supraglottic structures. There appears to be variability in the degree and topography of laryngeal muscle involvement, and the type of laryngeal dystonia seen clinically may actually represent a predominance of either adductor or abductor activity.⁸

The majority of dystonias are primary, or of idiopathic etiology. These patients have a normal perinatal and early developmental history; no prior history of head trauma or neurologic illness; no exposure to drugs known to cause acquired dystonia (e.g., phenothiazines); and normal intellectual, pyramidal, cerebellar, and sensory examinations. Identification of any cause by history, examination, or laboratory studies defines secondary dystonia. Most cases of spasmodic dysphonia present as focal laryngeal dystonias. A small number of these cases may be associated with or progress to symptoms in another part of the body. Although in our experience this is a small percentage, rates as high as 17% have been reported.⁷ Multiple factors have been noted to cause secondary spasmodic dystonia (Table 6.1). These may include neurologic disorders, drug exposures, and parkinsonism.

Spasmodic dysphonia can be further divided into abductor and adductor dysphonia. In adductor spasmodic dysphonia, patients present with a choked, strain-strangled voice, breaks in phonation, diminished volume, and a monotonal pitch. Patients with the abductor type present with a breathy, effortful voice, abrupt breaks in fluency, and whispered elements of speech. With severe spasms, patients may be aphonic. Compensatory behaviors may mask the patient’s true voice pattern. Patients with a severe adductor spasmodic dysphonia may exhibit compensatory abductor voicing, with aphonia or whispering.⁹ Some authors believe that all patients with spasmodic dysphonia have abductor and adductor contributions, with symptoms manifesting according to the predominant type.^10,11

In both groups, patients may demonstrate a phonation-associated tremor. In contrast to essential tremor, the spasmodic dysphonia–associated tremor is irregular and may be secondary to posturing of dystonic muscles in a position in which the agonist contractions do not fully neutralize those of the antagonist muscles. Blitzer and colleagues¹² showed that 25% of spasmodic dysphonia patients may have such a tremor.

Table 6.1 Etiologies of Dystonia

The diagnosis of spasmodic dysphonia is based on perceptual analysis of the voice with a characteristic pattern of vocal spasms, the absence of secondary causes, normal peripheral nerve supply, and intact swallowing and breathing functions of the larynx. Evaluation should include a detailed head and neck and neurologic examination, with particular attention paid to spasm, dysfunction, or tremor in any area of the head and neck. This examination should include flexible laryngoscopy with particular attention to glottal function for vowel sounds, disruptions, spasms, breathy breaks, and tremor with connected speech segments. We prefer flexible laryngoscopy to the rigid telescope because the larynx is positioned in a more neutral natural posture during the examination. This allows for a fuller assessment of extrinsic muscle hyperfunction, tremor, and dystonic movements during speech. The rigid telescope still has improved magnification and light for the detailed evaluation of the vibratory margin of the vocal fold, and has an appropriate place in the evaluation to exclude mucosal wave pathology. Leonard and Kendall13 noted that motion abnormalities in spasmodic dysphonia were present only during specific speaking actions, whereas they were present at all times with muscle tension dysphonia.

The recognition of intermittent hyperfunctional breaks and spasms, with excessive and inappropriate adduction or abduction of the vocal folds during specific vocal tasks, is the basis for the diagnosis of spasmodic dysphonia. The spasms and breaks have a characteristic and reproducible pattern that can be elicited using a standardized set of sentences. During the endoscopic laryngeal exam, adductor-type spasmodic dysphonia should demonstrate intermittent, occasionally more sustained, visible hyperadductory postures with hyperfunctional closure of the true or false vocal folds, excessive medial rotation of the vocalis process, or excessive vocal fold tension that corresponds to the chocked, strain-strangled voice breaks. The adductor spasms typically occur with phonation of vowels. The laryngeal exam for abductor-type spasmodic dysphonia should exhibit rapid and hyperfunctional abduction during the breathy voice breaks, which results in a breathy, although effortful, voice quality with aphonic whispered segments. Abductor spasms are marked when trying to phonate a vowel after a voiceless consonant (example /h/, /p/, or /t/). This is in contrast to other causes of a breathy voice such as vocal fold paralysis or presbylarynges, which should give a constant breathy quality to the voice. The diagnosis sometimes can be difficult because of the presence of tremor and overlying functional or compensatory postures that the patient has developed, and a repeat examination after a short course of voice therapy may be useful. The most effective method for training to recognize spasmodic dysphonia is through repeated exposure to a variety of different voices.

Ludlow and colleagues proposed a three-tier system for the diagnosis of spasmodic dysphonia. Tier one is a screening questionnaire that consists of four questions (Table 6.2). Patients are expected to have had symptoms for at least 3 months and answer in the affirmative to the first two questions to be considered as having possible spasmodic dysphonia. Tier two is a clinical speech examination in which patients are taken through a series of vocal exercises by a voice specialist. Specific sentences are used to elicit abductor and adductor voice breaks. Patients are expected to have one or more voice breaks during speaking and fewer during whispering to be included. Tier three, fiberoptic laryngoscopy, reveals normal glottal function with swallowing, whistling, and coughing while demonstrating vocal fold spasm, or tremor while speaking sentences. Using this three-tiered technique on a series of 30 patients with known muscle tension dysphonia, spasmodic dysphonia, or tremor, Ludlow and colleagues¹⁴ were able to correctly categorize 97% of patients.

Objective testing and other diagnostic modalities can be useful in assisting in the diagnosis of difficult cases. In assessing the utility of acoustic analysis, Zwirner and coworkers¹⁵ found significantly higher mean values of standard deviation of fundamental frequency, jitter, shimmer, and voice break factor, and significantly lower mean values of signal-to-noise ratio in spasmodic dysphonia patients when compared with normal controls. Using acoustic analysis, Sapienza and coworkers16 found that only patients with adductor spasmodic dysphonia manifested voice breaks during speech, specifically with sustained vowels. They also found patients with adductor spasmodic dysphonia to have greater variation in the type of acoustic event produced as a function of speech task. Koufman¹⁷ found spectral analysis to be useful in differentiating adductor spasmodic dysphonia and muscle tension dysphonia (MTD), sometimes a challenging task given the supraglottic hyperfunction that may be present in both processes. Koufman noted that voice breaks were usually present in spasmodic dysphonia but absent in MTD. The spasmodic dysphonia patients also had well-defined formants, whereas the MTD patients did not, and the MTD patients had excessive high-frequency spectral noise that was minimal in spasmodic dysphonia patients.¹⁷ This showed that spectral analysis, although not a frequently used tool, could potentially be a useful adjunct to differentiate adductor spasmodic dysphonia from muscle tension dysphonia.

Table 6.2 Screening Questions for Spasmodic Dysphonia38

Laryngeal electromyography (EMG) is also a potential adjunct in the diagnosis of adductor spasmodic dysphonia. Typically, EMG demonstrates abnormal, but not pathognomonic, large and polyphasic motor unit potentials and an abnormally long latency from the initiation of electrical signal to the beginning of sound production.^18,19 Nash and Ludlow²⁰ compared laryngeal EMG results in patients with adductor spasmodic dysphonia against controls. They found a significant increase in mean muscle activity during voice breaks in the thyroarytenoid muscle, whereas muscle tone in these patients was equivalent to controls during normal speech. Hillel8 used laryngeal EMG to examine 11 patients without laryngeal pathology, and then compared these findings with those of 59 patients with abductor, adductor, mixed, and tremor spasmodic dysphonia. He discovered “abnormal patterns of response, increased latencies, and increased amplitudes of recruitment in many tasks including nonphonatory tasks” among all spasmodic dysphonia patients. He also demonstrated abnormal activity in all five intrinsic laryngeal muscles, demonstrating substantially complex and variable dysfunction in the vocal musculature leading to the manifestations of spasmodic dysphonia. This implies that spasmodic dysphonia is a much more heterogeneous disorder than the simple classification of abductor and adductor spasmodic dysphonia suggests. Although evidence as noted above appears promising, the Laryngeal EMG Task Force’s recommendations on laryngeal EMG concludes that further data are needed to assess the reliability of this tool in the diagnosis of spasmodic dysphonia.²¹

The diagnosis of spasmodic dysphonia can be made reliably with the patient’s history and physical examination. Acoustic analysis and laryngeal EMG both have shown promise as aids for difficult cases, but more research is required to better define their role. The cornerstone of diagnosis at this time remains a carefully directed history with appropriate screening questions, speech examination, and flexible laryngoscopy.

Treatment

Botulinum Neurotoxin Treatment for Spasmodic Dysphonia

Botulinum neurotoxin type A injections into the intrinsic laryngeal muscles represent the current standard treatment for the treatment of spasmodic dysphonia. There have been over 100 published articles investigating the utility of BoNT injections for spasmodic dysphonia, with the collective evidence overwhelmingly favoring the effectiveness of this modality.

In 1998, Blitzer et al²² reported on their 12-year experience of BoNT treatment for spasmodic dysphonia. They found that 90% of patients improved for 3 to 12 months after injection of BoNT/A, with a need for repeat injections every 3 to 6 months. Two meta-analyses have been performed that considered the efficacy of BoNT, and one blinded, randomized controlled trial has been conducted in which BoNT injection was compared with saline injection and measured with objective acoustic outcomes.^23–25 BoNT/A markedly reduced perturbation, decreased fundamental frequency range, and improved spectrographic characteristics.

Although the main effect of BoNT is a blockade of the injected muscle at the neuromuscular junction in the peripheral nervous system, this explanation does not seem to correlate with the pathophysiologic model of spasmodic dysphonia or the rather surprising efficacy of this injection, suggesting an effect on the central nervous system. Byrnes and colleagues26 showed that BoNT injections caused a transient change in the mapping of muscle representation areas in the motor cortex. This has further been suggested by the effect of BoNT on noninjected laryngeal muscles in spasmodic dysphonia.²⁷ In 2007, Antonucci et al²⁸ demonstrated that BoNT is trans-located to the afferent synapses in the contralateral hemisphere in mice and rats.²⁸ Although these mechanisms are not completely understood, the efficacy and safety of BoNT have led to its being deemed the primary therapy for spasmodic dysphonia.

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