BT is reconstituted with saline before injection. A limited dilution volume is helpful since large amounts of injected volume harbor a higher risk of adverse effects as dysphagia. Typical amounts of saline are 2 ml/100 U of onabotulinum toxin (Botox^©, Allergan). The amount of BT needed is unique in each patient; accordingly a standard injection amount does not exist. Typical amounts range between 1 and 5 U of Botox to each side for effect in adductor-type SD. The amount should be titrated at each visit and be well documented. In a large series, the dose range varied between 0.008 and 30 U, with an average of 3 U [6]. A feasible starting dose could be 1 or 1.25 U of Botox per TA muscle. For patients with abductor-type SD, the dose is higher, e.g., 5 U as starting dose. In a retrospective case review of 100 injections, 2.5–7.5 U (mean 4.7 U total dose per patient) was found to be safe with a complication rate below 5% [22]. The long-term BT dose in 150 treatments has been reported to be very consistent with a trend downward over time [23]. The optimal dose normally is found after 2–3 treatments.

Immediately after the injection, a mild edema or hematoma can be expected. BT is effective after a latency time between 2 and 5 days. The major adverse reaction is breathiness together with onset of BT effect; a duration of 4–6 weeks can be expected in case of overdosage. Transient difficulty in swallowing liquids also is a common treatment side effect, reported to be present in 15–50% of the patients [24, 25]. To summarize, technically, there are no side effects, BT might be ineffective in case of underdosing, or benefit will only last for a shorter time. In case of overdosage, the injection will result in longer-lasting relief, but the side effects appear in a dose-dependent proportion. Breathiness after the BT injection goes in line with a longer-lasting relief of symptoms. Improper localization or deposition of the toxin too far behind into the larynx will enhance the risk of swallowing disorders after the procedure. Severe adverse events include bilateral abductor paralysis; the risk of stridor after bilateral injection has been numbered 8/352 (2.3%) with one patient needing a tracheotomy in a retrospective review [26]. The rule of thumb is 4–6 weeks after the injection, adverse effects always will disappear.

Symptoms of SD frequently improve on sedatives such as alcohol and benzodiazepines. Generally, oral drug treatment might be considered as an additional option, however, without expecting significant benefit. Baclofen is a GABA receptor agonist; there are no controlled studies to guide recommendations for its use, but retrospective studies and anecdotal experience suggest it is most often useful in childhood-onset dystonias, especially those with concomitant spasticity. Some adults also enjoy benefits from oral treatment, although most do not. The use of anticholinergics is often limited by peripheral and central side effects. Further medications that showed positive results include diphenhydramine, benztropine, and antiparkinson agents. To summarize, no pharmacological agent provides significant relief of SD. Even when success is noticed, their use is often limited due to side effects.

A definitive surgical approach for adductor-type SD is microlaryngoscopic resection of both thyroarytenoid muscles. Significant improvement has been reported in seven Japanese patients [27] and later with longer follow-up in further 15 patients [28]. Moderate and marked vocal improvement after 31 months of follow-up has been reported in up to 90% of the patients in a larger sample [29]. Earlier, TA muscle removal together with partial removal of the lateral cricoarytenoid muscle under local anesthesia has been reported with favorable outcome [30]. Laser vaporization of TA muscle has recently been reported with good results after 48 months of follow-up [31].

Type II thyroplasty, also called lateralization thyroplasty, has been proposed for treatment of SD in six patients by Isshiki and coworkers [32]. The authors later reported successful treatment in 41 patients after implanting a titanium bridge with 70% of the patients judging their voice as excellent and the remaining patients as improved to good or fair. Advantages of thyroplasty are reported to be unlikely recurrence, reversibility, no damage to the function of phonation, and the ability to perform readjustments [33]. High rates of early and late failures after 1-year follow-up later (only one-third of patients with marked improvement after 1-year follow-up) led to questioning of thyroplasty by a different group of surgeons [34]. Recently, myectomy and widening thyroplasty have been compared in a retrospective study in 35 patients. The authors reported that myectomy led to better voice quality in line with increased breathiness after the surgery [35].

Recurrent laryngeal nerve surgery is a third reported option. Transection of one recurrent nerve has been reported early [36]. Later, selective laryngeal adductor denervation combined with ansa cervicalis transfer and anastomosis to prevent total atrophy of TA muscles has been reported with good results [37, 38]. Chronic breathiness has been reported to be more likely in men. Adjuvant removal of TA muscle therefore has been recommended in women in case of recurrence [39].

Surgery for SD has even been reported to even result in better voice in comparison to BT treatment; however, the BT sample was small and the study design was retrospective [40]. To summarize, voice breaks can be effectively reduced by surgery, although severe hoarseness may result and long-term results are not yet predictable. Follow-up is crucial since there is a high risk of symptom recurrence within 5 years. Currently, surgery might therefore be considered in patients that cannot be provided with BT, refuse BT treatment, or are refractory to BT.

SD is a chronic dystonia; a clear delineation from functional voice disorders can be difficult. Voice disorders frequently include or interfere with psychological disorders [41], and functional voice disorders can respond to voice or behavioral therapies; hence, a trial of voice therapy might be recommended before or in line with BT injections. However, dystonia of the larynx does normally not respond to voice therapy, a fact that also has been demonstrated in a prospective controlled trial [42]. One study addressed the role of behavioral (speech) therapy in combination with BT injections with suggestion that behavioral treatment may enhance the effectiveness of BT injections [43]. Recently, five subjects were implanted with electrical implant into the TA muscle with promising immediate results [44]. Targeting the interventions proximal to the TA muscle are promising future research projects.

A large number of articles have described the effectiveness of BT for the improvement of vocal symptoms in SD. However, the applied methods for outcome measurements are extremely variable in the literature. Measured variables include perceptual analysis and electroglottographic-myographic, acoustic, endoscopic, and stroboscopic evaluation. Further variables are duration of benefit, aerodynamics, and subjective ratings [17]. A telephone screening tool with standardized utterances with high interrater reliability can be used during follow-up. Outcome measures as possible should include acoustic function via computerized analysis, perception analysis, as well as aerodynamic function (Table 8.1). Literature with comparison of treatment versus no treatment is rare. Improvement of fundamental frequencies, self-ratings of improvement, and spectrographic ratings were documented in one placebo-controlled trial [45]. In a longitudinal study of adductor-type SD, an initial breathy phase could be distinguished from a late declining phase during a mean duration of one injection cycle of 26 weeks [46].