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vocal tremor, such as dystonia and Parkinson’s disease, is the first step in diagnosis; and management of this condition and all patients should be evaluated by a neu rologist specializing in movement disorders and trialed on systemic oral medications. Oral medications may be effective in reducing symptoms in up to 50% of EVT patients. 16–21 As demonstrated in this study, targeted clinical examination allows the physician to pinpoint which areas may benefit from directed botulinum toxin injection, with the aim of reducing amplitude of laryn geal vibration and improving symptom control in patients who fail or inadequately respond to oral ther apy. We present an algorithm for observation and man agement of EVT to be used as a guide by practitioners treating this condition. During initial examination, the patient’s body habi tus should be observed for abnormal motion or postur ing. It is useful to examine handwriting on collected intake forms to look for signs of hand tremor. The head and neck should be carefully observed for abnormal movement at rest and during speech, and careful video laryngoscopy performed to identify areas of maximal tremor. Important questions to answer during examina tion are: “Is the tremor primarily horizontal at the glot tal level or is the tremor predominantly vertical with larynx moving up and down in the resonating cavity?”; “Are oscillatory movements of the head and neck con tributing to laryngopharyngeal movement?”; and “Is tremor present during both phonation and respiration?” Botulinum toxin therapy can then be targeted to the maximally affected region(s). EVT is often confused with spasmodic dysphonia, especially due to the incorrect but generally accepted view that EVT cannot exist in isolation of any other signs and symptoms of essential tremor. EVT is not task-specific and does not respond to sensory tricks. In addition, a family history is likely to be elicited on his tory in one-third to one-half of patients. 2 The tremor in spasmodic dysphonia (an agonist-antagonist dystonic tremor) is almost always an irregular, task-specific tremor (e.g., occurring with speaking or singing), and is unlikely to have significant vertical component. 12 Both disorders may improve with alcohol ingestion. 29 As demonstrated in the current study, EVT symp toms are most commonly caused by horizontal glottic tremor (94%). Such tremor can be reduced in amplitude (though not completely eliminated) through botulinum toxin-induced chemo-denervation of the thyroarytenoid/ posterior cricoarytenoid muscles. This procedure can be performed easily and repeatedly in the office under EMG guidance. Side effects such as breathiness and dysphagia are transient and last only 3 to 4 months until the toxin is destroyed. They can be minimized by low initial dosing regimes and correct needle place ment. Vertical laryngeal tremor secondary to alternat ing laryngeal elevation and descent can occur due to movement in both pharyngeal constrictor and strap muscles. Botulinum toxin injection to these muscles can reduce tremor amplitude and improve symptoms; however, needle placement is important to minimize risk of dysphagia. This can occur when injections are
TABLE II. Botulinum Toxin Treatment Characteristics.
N (%)
Muscles treated Thyroarytenoid
15 (93.8)
Strap muscles
7 (43.8)
Sternocleidomastoid
1 (6.3)
External pterygoid 1
(6.3)
Platysma
1 (6.3) 1 (6.3)
Posterior cricoarytenoid
Mean (SD)
Botulinum toxin initial dose (units per side) Thyroarytenoid
1.0 (0.6)
Strap muscles
3.2 (1.7)
Sternocleidomastoid
10
External pterygoid
7.5
Platysma
2.5
Posterior cricoarytenoid (unilateral)
3.75
Total number of injections
26.6 (15.5)
Total duration of treatment (years)
6.7 (3.1)
SD 5 Standard deviation
tremor. Eight subjects had concurrent dystonia with dys tonic tremor in addition to EVT.
Treatment Response and Side Effects All patients analyzed in this series had a response to botulinum toxin treatment, and 15 patients had undergone > 20 treatments over time (mean 26.6). Symp tom severity waxed and waned over time, and dose adjustments were frequently required according to the management paradigm outlined above. Eight of the 15 patients receiving thyroarytenoid injections had mild postinjection hoarseness lasting between 3 to 8 days without associated aspiration or dysphagia. There were no reported side effects of treatment from those patients receiving strap muscle injection.
Management Algorithm A management algorithm for EVT based is pre sented in Figure 1.
DISCUSSION Prevalence of essential tremor is estimated between 0.4% and 5.6% of the population over 40 years of age, reaching 15% after age 65. 8,25–29 Incidence of isolated EVT, the phonatory manifestation of ET, is between 0.3% and 1%, however; this may be an underestimation as many still believe that voice symptoms appear late and are secondary to the main features of ET. 2,13,19 EVT is due to involuntary oscillation of the muscles of speech production, which leads to rhythmic alternations in pitch and loudness. 2,12 Differentiation from other causes of
Laryngoscope 123: October 2013
Sinclair et al.: Botulinum Toxin Injection for Essential Vocal Tremor 2499
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